Scanning system

ABSTRACT

An example particle therapy system includes: a particle accelerator to output a beam of charged particles; and a scanning system to scan the beam across at least part of an irradiation target. An example scanning system includes: a scanning magnet to move the beam during scanning; and a control system (i) to control the scanning magnet to produce uninterrupted movement of the beam over at least part of a depth-wise layer of the irradiation target so as to deliver doses of charged particles to the irradiation target; and (ii) to determine, in synchronism with delivery of a dose, information identifying the dose actually delivered at different positions along the depth-wise layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 15/492,132, which was filed on Apr. 20, 2017; U.S. patent application Ser. No. 15/492,132 being a continuation of U.S. patent application Ser. No. 14/184,990, which was filed on Feb. 20, 2014, and which issued as U.S. Pat. No. 9,661,736 on May 23, 2017. The contents of U.S. patent application Ser. No. 15/492,132 and of U.S. patent application Ser. No. 14/184,990 are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates generally to a particle beam scanning system for use, e.g., with a particle therapy system.

BACKGROUND

Particle therapy systems use an accelerator to generate a particle beam for treating afflictions, such as tumors. In operation, particles are accelerated in orbits inside a cavity in the presence of a magnetic field, and are removed from the cavity through an extraction channel. A magnetic field regenerator generates a magnetic field bump near the outside of the cavity to distort the pitch and angle of some orbits so that they precess towards, and eventually into, the extraction channel. A beam, comprised of the particles, exits the extraction channel.

A scanning system is down-beam of the extraction channel. In this context, “down-beam” means closer to an irradiation target (here, relative to the extraction channel). The scanning system moves the beam across at least part of the irradiation target to expose various parts of the irradiation target to the beam. For example, to treat a tumor, the particle beam may be “scanned” over different cross-sectional layers of the tumor.

SUMMARY

An example particle therapy system comprises: a particle accelerator to output a beam of charged particles; and a scanning system to scan the beam across at least part of an irradiation target. An example scanning system comprises: a scanning magnet to move the beam during scanning, where a position of the beam corresponds to a current of the scanning magnet; and a control system (i) to control the current in order to produce uninterrupted movement of the beam across at least part of an irradiation target to deliver doses of charged particles, (ii) for positions at which the particle beam delivers dose, to store information identifying a location and an amount of dose delivered, (iii) to compare a cumulative dose delivered at each position to a target cumulative dose, and (iv) if the cumulative dose does not match the target cumulative dose at specific positions, control the current in order to move the beam so as to deliver additional dose to the specific positions. The example particle therapy system may include one or more of the following features, either alone or in combination.

An example particle accelerator includes an accelerator that may be configured to output pulses of charged particles in accordance with a radio frequency (RF) cycle. The pulses of charged particles form the beam. Movement of the beam across the at least part of an irradiation target may not be dependent upon the RF cycle. The control system may be configured to measure the cumulative dose delivered at each position. The measuring may be substantially synchronous with the RF cycle. The control system may be configured to measure the cumulative dose delivered at each position. The measuring may be substantially synchronous with delivery of dose at each position.

The information identifying a location and an amount of dose delivered may comprise an amount of dose delivered at each position and at least one of: a location of each position within the irradiation target or a magnet current corresponding to each position within the irradiation target. The location may correspond to three-dimensional coordinates within the irradiation target.

The particle therapy system may comprise: memory to store a treatment plan that identifies, for each position, a target cumulative dose of the particle beam. The treatment plan may omit information about individual doses delivered to individual positions during scanning.

The scanning system may comprise: a degrader to change an energy of the beam prior to output of the beam to the irradiation target. The degrader may be down-beam of the scanning magnet relative to the particle accelerator. The control system may be configured to control movement of at least part of the degrader into, or out of, a path of the beam in order to affect the energy of the beam and thereby set a layer of the irradiation target to which charged particles are to be delivered.

The particle accelerator may comprise an ion source to provide plasma from which pulses in the beam are extracted. During at least part of the movement of the degrader, the ion source may be deactivated.

The particle accelerator may comprise: an ion source to provide plasma from which pulses in the beam are extracted; and a voltage source to provide a radio frequency (RF) voltage to a cavity to accelerate particles from the plasma. The cavity may have a magnetic field for causing particles accelerated from the plasma column to move orbitally within the cavity. During at least part of the movement of the degrader, the voltage source may be deactivated. During the at least part of the movement of the degrader, the particle source may be deactivated at all or part of a same time that the voltage source is deactivated.

The particle accelerator may be a variable-energy particle accelerator. The control system may be configured to set an energy level of the particle accelerator prior to scanning. The control system may be configured to set an energy level of the particle accelerator during scanning.

For a position at which the particle beam delivers dose, each individual delivery of dose may be a percentage of the total cumulative dose. The percentage may be less than 100% of the total cumulative dose. The percentage may be about, or exactly, 100% of the total cumulative dose.

The scanning magnet may have an air core, a ferromagnetic core, or a core that is a combination of air and ferromagnetic material.

Another example particle therapy system comprises: a particle accelerator to output a beam of charged particles; and a scanning system to scan the beam across at least part of an irradiation target. An example scanning system comprises: a scanning magnet to move the beam during scanning; and a control system (i) to control the scanning magnet to produce uninterrupted movement of the beam over at least part of a depth-wise layer of the irradiation target so as to deliver doses of charged particles to the irradiation target; and (ii) to determine, in synchronism with delivery of a dose, information identifying the dose actually delivered at different positions along the depth-wise layer.

The example particle accelerator may be configured to output pulses of charged particles in accordance with a radio frequency (RF) cycle. The pulses of charged particles form the beam. Movement of the beam may not be dependent upon the RF cycle.

Another example particle therapy system comprises: a particle accelerator to output a beam of charged particles; and a scanning system to scan the beam across at least part of an irradiation target. An example scanning system comprises: a scanning magnet to move the beam during scanning, where a position of the beam corresponds to a current of the scanning magnet; and an open loop control system (i) to control the current to produce uninterrupted movement of the particle beam across at least part of a layer of an irradiation target, (ii) to record, in synchronism with delivery, doses of the particle beam delivered to the irradiation target and at least one of: coordinates at which the doses were delivered or magnet currents at which the doses were delivered, and (iii) to compensate for deficiencies in the recorded doses relative to corresponding target cumulative doses. The example particle therapy system may include one or more of the following features, either alone or in combination.

The particle accelerator may comprise: a voltage source to provide a radio frequency (RF) voltage to a cavity to accelerate particles from a plasma column, where the cavity has a magnetic field for causing particles accelerated from the plasma column to move orbitally within the cavity; an extraction channel to receive the particles accelerated from the plasma column and to output the received particles from the cavity towards the scanning system; and a regenerator to provide a magnetic field bump within the cavity to thereby change successive orbits of the particles accelerated from the plasma column so that, eventually, particles output to the extraction channel. The magnetic field may be between 4 Tesla (T) and 20 T and the magnetic field bump may be at most 2 Tesla. The uninterrupted movement of the particle beam across the at least part of the layer of the irradiation target may not be dependent upon the RF frequency.

The scanning magnet may comprise an air core. The particle therapy system may comprise a gantry on which the particle accelerator and the scanning system are mounted. The gantry may be configured to move the particle accelerator and the scanning system around the irradiation target. The current of the scanning magnet may be adjusted based on a position of the gantry.

The particle accelerator may comprise a synchrocyclotron. Uninterrupted movement of the particle beam may occur across an entirety of the layer or across less than an entirety of the layer.

The particle therapy system may comprise a current sensor associated with the scanning magnet. Recording coordinates at which the doses were delivered may comprise sampling an output of the current sensor and correlating the output to coordinates. The particle therapy system may comprise an ionization chamber between the scanning magnet and the irradiation target. Recording doses of the particle beam delivered to the irradiation target may comprise sampling an output of the ionization chamber for each close.

An example proton therapy system may include any of the foregoing particle accelerators and scanning systems; and a gantry on which the particle accelerator and scanning system are mounted. The gantry may be rotatable relative to a patient position. Protons may be output essentially directly from the particle accelerator and through the scanning system to the position of an irradiation target, such as a patient. The particle accelerator may be a synchrocyclotron.

Two or more of the features described in this disclosure, including those described in this summary section, may be combined to form implementations not specifically described herein.

Control of the various systems described herein, or portions thereof, may be implemented via a computer program product that includes instructions that are stored on one or more non-transitory machine-readable storage media, and that are executable on one or more processing devices (e.g., microprocessor(s), application-specific integrated circuit(s), programmed logic such as field programmable gate array(s), or the like). The systems described herein, or portions thereof, may be implemented as an apparatus, method, or electronic system that may include one or more processing devices and computer memory to store executable instructions to implement control of the stated functions.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are a cross-sectional views of an example synchrocyclotron for use in a particle therapy system.

FIG. 3 is a side view of an example scanning system.

FIG. 4 is a perspective view of components of an example scanning system.

FIG. 5 is a front view of an example magnet for use in a scanning system of the type shown in FIGS. 3 and 4 .

FIG. 6 is a perspective view of an example magnet for use in a scanning system of the type shown in FIGS. 3 and 4 .

FIG. 7 is a perspective view of an example energy degrader (range modulator) for use in a scanning system of the type shown in FIGS. 3 and 4 .

FIG. 8 is a perspective view of a process for moving a plate of an energy degrader in the path of a particle beam.

FIG. 9 is a flowchart showing an example process for performing raster scanning that may be performed using the hardware of FIGS. 1 to 8 .

FIG. 10 is a top view show an example cross-section of an irradiation target and a radiation scan path.

FIG. 11 is a perspective view of an example therapy system.

FIG. 12 is an exploded perspective view of components of an example synchrocyclotron for use in the particle therapy system.

FIG. 13 is a cross-sectional view of the example synchrocyclotron.

FIG. 14 is a perspective view of the example synchrocyclotron.

FIG. 15 is a cross-sectional view of an example ion source for use in the synchrocyclotron.

FIG. 16 is a perspective view of an example dee plate and an example dummy dee for use in the synchrocyclotron.

FIG. 17 shows a patient positioned within an example inner gantry of the example particle therapy system in a treatment room.

FIG. 18 is a conceptual view of an example particle therapy system that may use a variable-energy particle accelerator.

FIG. 19 is a perspective, exploded view of an example magnet system that may be used in a variable-energy particle accelerator.

FIG. 20 is an example graph showing energy and current for variations in magnetic field and distance in a particle accelerator.

FIG. 21 is a side view of an example structure for sweeping voltage on a dee plate over a frequency range for each energy level of a particle beam, and for varying the frequency range when the particle beam energy is varied.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Described herein is an example of a particle accelerator for use in a system, such as a proton or ion therapy system. The example particle therapy system includes a particle accelerator—in this example, a synchrocyclotron—mounted on a gantry. The gantry enables the accelerator to be rotated around a patient position, as explained in more detail below. In some implementations, the gantry is steel and has two legs mounted for rotation on two respective bearings that lie on opposite sides of a patient. The particle accelerator is supported by a steel truss that is long enough to span a treatment area in which the patient lies and that is attached at both ends to the rotating legs of the gantry. As a result of rotation of the gantry around the patient, the particle accelerator also rotates.

In an example implementation, the particle accelerator (e.g., the synchrocyclotron) includes a cryostat that holds one or more superconducting coils, each for conducting a current that generates a magnetic field (B). In this example, the cryostat uses liquid helium (He) to maintain each coil at superconducting temperatures, e.g., 4° Kelvin (K). Magnetic yokes or smaller magnetic pole pieces are located inside the cryostat, and define a cavity in which particles are accelerated.

In this example implementation, the particle accelerator includes a particle source (e.g., a Penning on Gauge—PIG source) to provide a plasma column to the cavity. Hydrogen gas is ionized to produce the plasma column. A voltage source provides a radio frequency (RF) voltage to the cavity to accelerate pulses of particles from the plasma column.

As noted, in an example, the particle accelerator is a synchrocyclotron. Accordingly, the RF voltage is swept across a range of frequencies to account for relativistic effects on the particles (e.g., increasing particle mass) when accelerating particles from the plasma column. The magnetic field produced by running current through a superconducting coil causes particles accelerated from the plasma column to accelerate orbitally within the cavity. In other implementations, a particle accelerator other than a synchrocyclotron may be used. For example, a cyclotron, a synchrotron, a linear accelerator, and so forth may be substituted for the synchrocyclotron described herein.

In the example synchrocyclotron, a magnetic field regenerator (“regenerator”) is positioned near the outside of the cavity (e.g., at an interior edge thereof) to adjust the existing magnetic field inside the cavity to thereby change locations (e.g., the pitch and angle) of successive orbits of the particles accelerated from the plasma column so that, eventually, the particles output to an extraction channel that passes through the cryostat. The regenerator may increase the magnetic field at a point in the cavity (e.g., it may produce a magnetic field “bump” at an area of the cavity), thereby causing each successive orbit of particles at that point to precess outwardly toward the entry point of the extraction channel until it reaches the extraction channel. The extraction channel receives particles accelerated from the plasma column and outputs the received particles from the cavity as a particle beam.

The superconducting (“main”) coils can produce relatively high magnetic fields. The magnetic field generated by a main coil may be within a range of 4 T to 20 T or more. For example, a main coil may be used to generate magnetic fields at, or that exceed, one or more of the following magnitudes: 4.0 T, 4.1 T, 4.2 T, 4.3 T, 4.4 T, 4.5 T, 4.6 T, 4.7 T, 4.8 T, 4.9 T, 5.0 T, 5.1 T, 5.2 T, 5.3 T, 5.4 T, 5.5 T, 5.6 T, 5.7 T, 5.8 T, 5.9 T, 6.0 T, 6.1 T, 6.2 T, 6.3 T, 6.4 T, 6.5 T, 6.6 T, 6.7 T, 6.8 T, 6.9 T, 7.0 T, 7.1 T, 7.2 T, 7.3 T, 7.4 T, 7.5 T, 7.6 T, 7.7 T, 7.8 T, 7.9 T, 8.0 T, 8.1 T, 8.2 T, 8.3 T, 8.4 T, 8.5 T, 8.6 T, 8.7 T, 8.8 T, 8.9 T, 9.0 T, 9.1 T, 9.2 T, 9.3 T, 9.4 T, 9.5 T, 9.6 T, 9.7 T, 9.8 T, 9.9 T, 10.0 T, 10.1 T, 10.2 T, 10.3 T, 10.4 T, 10.5 T, 10.6 T, 10.7 T, 10.8 T, 10.9 T, 11.0 T, 11.1 T, 11.2 T, 11.3 T, 11.4 T, 11.5 T, 11.6 T, 11.7 T, 11.8 T, 11.9 T, 12.0 T, 12.1 T, 12.2 T, 12.3 T, 12.4 T, 12.5 T, 12.6 T, 12.7 T, 12.8 T, 12.9 T, 13.0 T, 13.1 T, 13.2 T, 13.3 T, 13.4 T, 13.5 T, 13.6 T, 13.7 T, 13.8 T, 13.9 T, 14.0 T, 14.1 T, 14.2 T, 14.3 T, 14.4 T, 14.5 T, 14.6 T, 14.7 T, 14.8 T, 14.9 T, 15.0 T, 15.1 T, 15.2 T, 15.3 T, 15.4 T, 15.5 T, 15.6 T, 15.7 T, 15.8 T, 15.9 T, 16.0 T, 16.1 T, 16.2 T, 16.3 T, 16.4 T, 16.5 T, 16.6 T, 16.7 T, 16.8 T, 16.9 T, 17.0 T, 17.1 T, 17.2 T, 17.3 T, 17.4 T, 17.5 T, 17.6 T, 17.7 T, 17.8 T, 17.9 T, 18.0 T, 18.1 T, 18.2 T, 18.3 T, 18.4 T, 18.5 T, 18.6 T, 18.7 T, 18.8 T, 18.9 T, 19.0 T, 19.1 T, 19.2 T, 19.3 T, 19.4 T, 19.5 T, 19.6 T, 19.7 T, 19.8 T, 19.9 T, 20.0 T, 20.1 T, 20.2 T, 20.3 T, 20.4 T, 20.5 T, 20.6 T, 20.7 T, 20.8 T, 20.9 T, or more. Furthermore, a main coil may be used to generate magnetic fields that are within the range of 4 T to 20 T (or more, or less) that are not specifically listed above.

In some implementations, such as the implementation shown in FIGS. 1 and 2 , large ferromagnetic magnetic yokes act as a return for stray magnetic field produced by the superconducting coils. For example, in some implementations, the superconducting magnet can generate a relatively high magnetic field of, e.g., 4 T or more, resulting in considerable stray magnetic fields. In some systems, such as that shown in FIGS. 1 and 2 , the relatively large ferromagnetic return yoke 100 is used as a return for the magnetic field generated by superconducting coils. A magnetic shield surrounds the yoke. The return yoke and the shield together dissipated stray magnetic field, thereby reducing the possibility that stray magnetic fields will adversely affect the operation of the accelerator.

In some implementations, the return yoke and shield may be replaced by, or augmented by, an active return system. An example active return system includes one or more active return coils that conduct current in a direction opposite to current through the main superconducting coils. In some example implementations, there is an active return coil for each superconducting coil, e.g., two active return coils—one for each superconducting coil (referred to as a “main” coil). Each active return coil may also be a superconducting coil that surrounds the outside of a corresponding main superconducting coil.

Current passes through the active return coils in a direction that is opposite to the direction of current passing through the main coils. The current passing through the active return coils thus generates a magnetic field that is opposite in polarity to the magnetic field generated by the main coils. As a result, the magnetic field generated by an active return coil is able to dissipate at least some of the relatively strong stray magnetic field resulting from the corresponding main coil. In some implementations, each active return may be used to generate a magnetic field of between 2.5 T and 12 T or more. An example of an active return system that may be used is described in U.S. patent application Ser. No. 13/907,601, filed on May 31, 2013, the contents of which are incorporated herein by reference.

Referring to FIG. 3 , at the output of extraction channel 102 of particle accelerator 105 (which may have the configuration shown in FIGS. 1 and 2 ), is an example scanning system 106 that may be used to scan the particle beam across at least part of an irradiation target. FIG. 4 also shows examples of components of the scanning system. These include, but are not limited to, a scanning magnet 108, an ion chamber 109, and an energy degrader 110. Other components that may be incorporated into the scanning system are not shown in FIG. 4 , including, e.g., one or more scatterers for changing beam spot size.

In an example operation, scanning magnet 108 is controllable in two dimensions (e.g., Cartesian XY dimensions) to direct the particle beam across a part (e.g., a cross-section) of an irradiation target. Ion chamber 109 detects the dosage of the beam and feeds-back that information to a control system to adjust beam movement. Energy degrader 110 is controllable to move material (e.g., one or more individual plates) into, and out of, the path of the particle beam to change the energy of the particle beam and therefore the depth to which the particle beam will penetrate the irradiation target. In this way, the energy degrader selects a depth-wise layer of an irradiation target to scan in two dimensions.

FIGS. 5 and 6 show views of an example scanning magnet 108. In this example implementation, scanning magnet 108 includes two coils 111, which control particle beam movement in the X direction, and two coils 112, which control particle beam movement in the Y direction. Control is achieved, in some implementations, by varying current through one or both sets of coils to thereby vary the magnetic field(s) produced thereby. By varying the magnetic field(s) appropriately, the particle beam can be moved in the X and/or Y direction across the irradiation target. In some implementations, the scanning magnet is not movable physically relative to the particle accelerator. In other implementations, the scanning magnet may be movable relative to the particle accelerator (e.g., in addition to the movement provided by the gantry). In some implementations, the scanning magnet may be controllable to move the particle beam continuously so that there is uninterrupted motion of the particle beam over at least part of, and possibly all of, a layer of an irradiation target being scanned. In other implementations, the scanning magnets are controllable at intervals or specific times. In some implementations, there may be different scanning magnets to control all or part movement of a particle beam in the X and/or Y directions.

In some implementations, scanning magnet 108 may have an air core. In other implementations, scanning magnet 108 may have a ferromagnetic (e.g., an iron) core. In general, a magnet having an air core includes a magnetic coil around a core that is a non-ferromagnetic material, such as air. For example, an air core magnet may include self-supporting coils that surround air. In some implementations, an air core magnet may include coils that are wound around an insulator, such as ceramic or plastic, which may or may not include air.

In some cases, an air core may have advantages over a ferromagnetic core. For example, the amount that the particle beam moves (e.g., is deflected) in the X and/or Y directions is determined, at least in part, based on the amount of current applied to the magnet (referred to as the “magnet current”). A scanning magnet typically has a movement (or deflection) range, which is the extent over which the magnet will move the beam. At extremes of this range, such as at the edges, larger amounts of current are applied to the scanning magnet in order to achieve relatively high amounts of beam deflection. Some types of scanning magnets having a ferromagnetic core may saturate at these extremes, resulting in a non-linear relationship between current and magnet movement. That is, the amount of deflection produced by the magnet may not be linearly proportional to the amount of current applied to the magnet. Due to this non-linearity, in some cases, it may be difficult to determine and/or set some beam locations using magnet current. Accordingly, when a scanning magnet having a ferromagnetic core is used, there may need to be some calibration and/or compensation performed in order to correct for non-linearities such as that described above.

In contrast, a scanning magnet having an air core may not saturate in the same manner as a scanning magnet having a ferromagnetic core. For example, an air core magnet may not saturate or may saturate less than a magnet having a ferromagnetic core. As a result, the relationship between current and magnet movement may be more linear, particularly at the range extremes, making determinations of beam location based on magnet current more accurate, at least in some cases. This increased linearity also can enable more accurate movement of the beam, particularly at range extremes. That is, since the relationship between current and beam movement is generally more linear over a larger range when an air core scanning magnet is used, beam movement may be more easily reproducible using an air core scanning magnet. This can be advantageous, since a depth-wise layer of an irradiation target may require multiple scans, each providing a percentage of a total cumulative radiation close. Precision in delivery of multiple doses to the same area, such as that which can be obtained through use of an air core scanning magnet, can affect the efficacy of the treatment.

Although the relationship between current and magnet movement may be more linear in an air core magnet, in some cases, an air core magnet may be more susceptible to stray magnetic fields than a magnet having a ferromagnetic core. These stray magnetic fields may impact the scanning magnet during motion of the scanning magnet produced by the gantry. Accordingly, in some implementations that use a scanning magnet having an air core, the current applied to the scanning magnet to move the beam may be calibrated to account for the position of the scanning magnet relative to the patient (or, correspondingly, to account for the position of the gantry, since the position of the gantry corresponds to the position of the scanning magnet relative to the patient). For example, the behavior of the scanning magnet may be determined and, if necessary, corrected, for different rotational positions (angles) of the gantry, e.g., by increasing or decreasing some applied current based on rotational position.

In some implementations, the scanning magnet may have a core that is comprised of both air and a ferromagnetic material (e.g., iron). In such implementations, the amount and configuration of air and ferromagnetic material in the core may be determined taking the foregoing factors into account.

In some implementations, a current sensor 118 may be connected to, or be otherwise associated with, scanning magnet 108. For example, the current sensor may be in communication with, but not connected to, the scanning magnet. In some implementations, the current sensor samples current applied to the magnet, which may include current to coil(s) for controlling beam scanning in the X direction and/or current to coil(s) for controlling beam scanning in the Y direction. The current sensor may sample current through the magnet at times that correspond to the occurrence of pulses in the particle beam or at a rate that exceeds the rate that the pulses occur in the particle beam. In the latter case, the samples, which identify the magnet current, are correlated to detection of the pulses by the ion chamber described below. For example, the times at which pulses are detected using the ion chamber (described below) may be correlated in time to samples from the current sensor, thereby identifying the current in the magnet coil(s) at the times of the pulses. Using the magnet current, it thus may be possible to determine the location on the irradiation target (e.g., on a depth-wise layer of the irradiation target) where each pulse, and thus dose of particles, was delivered. The location of the depth-wise layer may be determined based on the position of the energy degrader (e.g., the number of plates) in the beam path.

During operation, the magnitude(s) (e.g., value(s)) of the magnet current(s) may be stored for each location at which a dose is delivered, along with the amount (e.g., intensity) of the close. A computer system, which may be either on the accelerator or remote from the accelerator and which may include memory and one or more processing devices, may correlate the magnet current to coordinates within the radiation target, and those coordinates may be stored along with the amount of the close. For example, the location may be identified by depth-wise layer number and Cartesian XY coordinates or by Cartesian XYZ coordinates (with the layer corresponding to the Z coordinate). In some implementations, both the magnitude of the magnet current and the coordinate locations may be stored along with the dose at each location. This information may be stored in memory either on, or remote from, the accelerator. As described in more detail below, this information may be used during scanning to apply multiple doses to the same locations to achieve target cumulative doses.

In some implementations, ion chamber 109 detects dosage (e.g., one or more individual doses) applied by the particle beam to positions on an irradiation target by detecting the numbers of ion pairs created within a gas caused by incident radiation. The numbers of ion pairs correspond to the dose provided by the particle beam. That information is fed-back to the computer system and stored in memory along with the time that the dose is provided. This information may be correlated to, and stored in association with, the location at which the dose was provided and/or the magnitude of the magnet current at that time, as described above.

As described in more detail below, in some implementations, the scanning system is run open loop, in which case the particle beam is moved freely and uninterrupted across an irradiation target so as to substantially cover the target with radiation. As the radiation is delivered, dosimetry implemented by the particle therapy control system records (e.g., stores) the amount of the radiation per location and information corresponding to the location at which the radiation was delivered. The location at which the radiation was delivered may be recorded as coordinates or as one or more magnet current values, and the amount of the radiation that was delivered may be recorded as dosage in grays. Because the system is run open loop, the delivery of the radiation is not synchronized to the operation of the particle accelerator (e.g., to its RF cycle). However, the dosimetry may be synchronized to the operation of the particle accelerator. More specifically, the dosimetry records the amount and location of each dose delivered as the dose is delivered (that is, as dose in time to delivery as possible given the limits of technology). Since the close is delivered in synchronism with the operation of the accelerator (e.g., one pulse is delivered per RF cycle), in some implementations, the dosimetry that records the dose and the location operates in synchronism, or substantially in synchronism, with delivery of radiation doses to the target, and thus in synchronism with the operation of the particle accelerator, such as its RF cycle.

FIG. 7 shows a range modulator 115, which is an example implementation of energy degrader 110. In some implementations, such as that shown in FIG. 7 , the range modulator includes a series of plates 116. The plates may be made of one or more of the following example materials: carbon, beryllium or other material of low atomic number. Other materials, however, may be used in place of, or in addition to, these example materials.

One or more of the plates is movable into, or out of, the beam path to thereby affect the energy of the particle beam and, thus, the depth of penetration of the particle beam within the irradiation target. For example, the more plates that are moved into the path of the particle beam, the more energy that will be absorbed by the plates, and the less energy the particle beam will have. Conversely, the fewer plates that are moved into the path of the particle beam, the less energy that will be absorbed by the plates, and the more energy the particle beam will have. Higher energy particle beams typically penetrate deeper into the irradiation target than do lower energy particle beams. In this context, “higher” and “lower” are meant as relative terms, and do not have any specific numeric connotations.

Plates are moved physically into, and out of, the path of the particle beam. For example, as shown in FIG. 8 , a plate 116 a moves along the direction of arrow 117 between positions in the path of the particle beam and outside the path of the particle beam. The plates are computer-controlled. Generally, the number of plates that are moved into the path of the particle beam corresponds to the depth at which scanning of an irradiation target is to take place. For example, the irradiation target can be divided into cross-sections or depth-wise layers, each of which corresponds to an irradiation depth. One or more plates of the range modulator can be moved into, or out of, the beam path to the irradiation target in order to achieve the appropriate energy to irradiate each of these cross-sections or depth-wise layers of the irradiation target. The range modulator may be stationary relative to the particle beam during scanning of a part of (e.g., cross-section of) an irradiation target, except for its plates moving in and out of the path of the particle beam. Alternatively, the range modulator of FIGS. 7 and 8 may be replaced with a range modulator that, at least some of the time, tracks movement of the particle beam, thereby enabling use of smaller plates.

In implementations that use a range modulator of the type described above, the number of plates that are moved into the beam path determine/set the depth-wise layer of the irradiation target that is to be scanned. For example, if two plates are moved into the beam path, the layer will be more shallow than if one or no plates are moved into the beam path. The layer may be identified, and stored in memory, based on the number of plates moved into the beam path. In some implementations, the plates may have different thicknesses. In such implementations, the thicknesses of the various plates also affect which layer is to be scanned (e.g., how deep the particle beam will penetrate the target).

In some implementations, the particle accelerator may be a variable-energy particle accelerator, such as the example particle accelerator described in U.S. patent application Ser. No. 13/916,401, filed on Jun. 12, 2013, the contents of which are incorporated herein by reference. In example systems where a variable-energy particle accelerator is used, there may be less need for an energy degrader of the type described herein, as the energy level of the particle beam may be controlled by the particle accelerator. For example, in some systems that employ a variable-energy particle accelerator, an energy degrader may not be needed. In some systems that employ a variable-energy particle accelerator, an energy degrader may still be used to change beam energy levels.

In some implementations, a treatment plan is established prior to treating the irradiation target. The treatment plan may be stored in memory that is accessible to a computer system that controls operation of the particle therapy system. The treatment plan may include information about how radiation treatment is to be provided by the particle therapy system. For example, the treatment plan may specify how scanning is to be performed for a particular irradiation target. In some implementations, the treatment plan specifies that raster scanning is to be performed. Raster scanning includes producing an uninterrupted movement of the particle beam across the irradiation target. For example, the scanning magnet moves continually to scan (e.g., move) the particle beam across the irradiation target so as to produce uninterrupted movement of the particle beam over at least part of a layer of an irradiation target. The movement may be uninterrupted across an entire layer of the irradiation target or across only part of a layer. In some implementations, the beam may be moved at a constant speed along all or part of a layer of the irradiation target. In some implementations, the speed at which the beam is moved along all or part of a layer of the irradiation target may vary. For example, the particle beam may move more quickly across internal portions of a layer than at edges of the layer. The speed of movement may be specified in the treatment plan.

In some implementations, the treatment plan may also specify the target cumulative dose of radiation (particles) to be applied to various positions on layers of an irradiation target. The dose is cumulative in the sense that it may be achieved through application of one or more doses of particles. For example, the same location (e.g., in XYZ space) on an irradiation target may be irradiated ten times, each time with 10% of the target cumulative dose to achieve the target cumulative dose. In some implementations, the treatment plan need not specify the amount of dose for each location, the locations, or the number of times that locations are to be irradiated. That is, this information may be omitted from the treatment plan in some implementations. Rather, in some implementations, the intensity of the particle beam may be set beforehand to provide a particular dose of radiation per instance of irradiation. The particle beam may then be scanned over a layer of the irradiation target in an open loop manner, without requiring feedback to move to a next location. As the particle beam is scanned, the location of the beam is determined and the corresponding dose at that location is determined. The determination may be made at about the same time as the scanning and delivery (that is, as dose in time to delivery as possible given the limits of technology). The cumulative dose at that location, which includes the current dose as well as any dose previously delivered during the current treatment, is compared to the target cumulative dose from the treatment plan. If the two do not match, then additional dose may be applied to that location during a subsequent scan. Since it is not always known precisely how much radiation will be delivered to a location per scan, the number of times that a location is scanned may not be set beforehand. Likewise, since there may be fluctuations in the amount of radiation actually delivered per scan to a location, the precise amount of radiation per scan is not necessarily set beforehand. Consequently, in some implementations, such information need not be included in the treatment plan.

In some implementations, the treatment plan may also include one or more patterns, over which the particle beam may be scanned per layer. The treatment plan may also specify the number of plates of an energy degrader to achieve a particular energy level/layer. Other implementations may include information in addition to, or instead of, that specified above.

In some implementations, the overall treatment plan of an irradiation target may include different treatment plans for different cross-sections (layers) of the irradiation target. The treatment plans for different cross-sections may contain the same information or different information, such as that provided above.

In some implementations, the scanning system may include a collimator 120 (FIG. 3 ) to collimate the particle bean, which may include an aperture that is placeable relative to the irradiation target to limit the extent of the particle beam and thereby alter the shape of the spot applied to the irradiation target. For example, the collimator may be placed in the beam path down-beam of the energy degrader and before the particle beam hits the irradiation target. The collimator may contain an area (e.g., a hole or a transmissive material) through which the particle beam passes and another material (e.g., brass) around the hole that inhibits or prevents passage of the particle beam.

In some implementations, the collimator may include a structure defining an edge. The structure may include a material, such as brass, that inhibits transmission of the particle beam. The structure may be controllable to move in two dimensions relative to the irradiation target so that at least part of the structure is between at least part of the particle beam and the irradiation target. For example, the structure may be movable in the X and Y directions of a plane that intersects the particle beam and that is parallel to, or substantially parallel to, a cross-section of the irradiation target that is being treated. Use of a collimator in this manner may be beneficial in that it can be used to customize the cross-sectional shape of the particle beam that reaches the patient, thereby limiting the amount of particle beam that extends beyond the radiation target. Examples of collimators and energy degraders that may be used are described in U.S. patent application Ser. No. 14/137,854, which was filed on Dec. 20, 2013, and which is incorporated herein by reference.

As noted above, in some implementations, scanning is performed in an open-loop manner, e.g., by an open-loop control system that may be implemented using one or more processing devices, such as the computing device that controls the particle therapy system. In this example, open-loop scanning includes moving the particle beam across an irradiation target to substantially cover the target with radiation. In some implementations, movement is not synchronized with operation of the accelerator, e.g., with the RF frequency, but rather runs independently of the operation of the accelerator when the accelerator is operating. For example, movement of the particle beam may be uninterrupted, and not dependent upon the RF cycle of the particle accelerator. Uninterrupted movement may occur across all or part of a layer of an irradiation target. However, as described herein, the dosimetry may be synchronized with delivery of pulses of the particle beam to the irradiation target. In examples where the dosimetry is synchronized with delivery of pulses of the particle beam, the dosimetry is also synchronized with operation of the accelerator (e.g., with the RF frequency used to draw pulses of the particle beam from the ion source plasma column).

The radiation level of an individual dose of particle beam (e.g., an individual pulse from the accelerator) may be set beforehand. For example, each individual dose may be specified in grays. An individual dose may be, or correspond to, a percentage of the target cumulative dose that is to be applied to a location (e.g., an XYZ coordinate) in an irradiation target. In some implementations, the individual dose may be 100% of the target cumulative dose and, as a result, only a single scan may be needed to deliver a single dose of radiation (e.g., one or more particle pulses) per location to the irradiation target. In some implementations, the individual dose may be less than 100% of the target cumulative dose, resulting in the need for multiple scans of the same location to deliver multiple doses of radiation to the irradiation target. The individual dose may be any appropriate percentage of the target cumulative dose, such as: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or any percentage in between these values.

The scanning magnet current may be controlled, in accordance with the treatment plan, to scan a depth-wise layer of the irradiation target. The layer is selected by appropriately positioning one or more energy degraders from the range compensator in the path of the particle beam and/or by setting an energy level of a variable-energy particle accelerator. As the layer is scanned, the current sensor samples the current applied to the scanning magnet. The amount of magnet current may be recorded, e.g., stored in memory. If more than one magnet or magnet coil is used, the amount of magnet current may be stored along with the identity of the magnet or coil. In addition, the current may be correlated to coordinates within the irradiation target (e.g., Cartesian XYZ coordinates) and those coordinates may be stored in addition to, or instead of, the corresponding magnet current. As explained above, the current sensor may sample the magnet current and correlate the sampling time to the time at which an irradiation dose (e.g., pulse) is delivered.

In this regard, ion chamber 109 may detect the intensity of doses delivered to the irradiation target as that dose is delivered. The intensity of each dose is recorded (e.g., stored in memory) along with the location of each delivered close. As noted, the location of each delivered dose may be stored by coordinates, magnet current, or using some other appropriate metric. As noted above, the dosimetry—the dose verification—may be synchronized with delivery of the close and, thus, with the output of the accelerator (which corresponds to the RF frequency, as described above). Accordingly, in some implementations, each time a dose is delivered, the intensity of that dose is determined almost immediately and the location at which the dose is applied is determined almost immediately. This information may be stored in one or more tables (e.g., one table per layer or multiple tables per layer) or other appropriate computer storage construct.

In some implementations, the tables may be updated as additional doses are delivered. For example, a table may keep a running track of the amount of dose delivered at each location. So, if the beam dose is “X” grays, at a first scan pass, the table may record X grays for a location. At a second scan pass, the table may record 2X grays, and so forth until the target cumulative dose is reached.

In this regard, for each location, a processing device associated with the accelerator (e.g., the computer system that controls the particle therapy system) may compare the cumulative dose from a table, such as that described above, to the target cumulative dose. If the cumulative dose matches the target cumulative dose, treatment for that location (or layer) is deemed completed. If the cumulative dose does not match the target cumulative dose, additional treatment is performed. For example, the layer or location is scanned again at the same locations, which are obtained from the table. The linear correlation between magnet current and beam movement produced by use of an air core magnet can facilitate repeated, and relatively accurate, repeated scanning at the same locations during multiple passes of the beam during scanning.

Scanning may be repeated, at the same locations, any appropriate number of times until the target cumulative dose is reached at each location. In this regard, the entire layer may be re-scanned or only select portions of the layer may be re-scanned, dependent upon the target cumulative doses for the different locations on the layer. In some implementations, the intensity of the particle beam is not varied between scans. In other implementations, the intensity of the particle beam may be varied between scans, particularly if a small dose is required to top-off a cumulative dose to reach the target cumulative dose. The intensity of the close may be increased or decreased, e.g., by altering the operation of the ion source (e.g., increasing the plasma ionization), altering the sweep of the RF frequency, or by any other appropriate methods. Examples of ways to vary the intensity of the dose are described in U.S. patent application Ser. No. 14/039,307, which was filed on Sep. 27, 2013, and which is incorporated herein by reference.

As noted, scanning may be repeated for an entire layer or for only a portion of a layer. In some implementations, an entire layer, or a portion thereof, may be fully treated before treating another layer. That is, scanning may be repeated until the total cumulative dose is reached for each location on a layer before another layer is treated. In some implementations, each layer may be treated partially (e.g., scanned once) in sequence, and then re-scanned in sequence. In some implementations, several designated layers may be completely treated before other layers are treated. In some implementations, the entire target may be scanned once, followed by successive scans of the entire target until the appropriate total cumulative dose is delivered to each location.

During movement between layers, the beam may be turned-off. For example, during movement between layers, the ion source may be turned-off, thereby disrupting the output of the beam. During movement between layers, the RF sweep in the particle accelerator may be turned-off, thereby disrupting the extraction (and thus output) of the beam. During movement between layers, both the ion source and the circuitry that creates the RF sweep may be deactivated in some implementations. In some implementations, rather than turning-off the ion source and/or the RF sweep during movement between layers, the beam may be deflected to a beam-absorbing material using a kicker magnet (not shown) or the scanning magnet.

Different cross-sections of the irradiation target may be scanned according to different treatment plans. As described above, an energy degrader is used to control the scanning depth. In some implementations, the particle beam may be interrupted or redirected during configuration of the energy degrader. In other implementations, this need not be the case.

Described herein are examples of treating cross-sections of an irradiation target. These may be cross-sections that are roughly perpendicular to the direction of the particle beam. However, the concepts described herein are equally applicable to treating other portions of an irradiation target that are not cross-sections perpendicular to the direction of the particle beam. For example, an irradiation target may be segmented into spherical, cubical or other shaped volumes, and those volumes may be treated using the example processes, systems, and/or devices described herein.

FIG. 9 is a flowchart showing an example implementation of the scanning process described herein. Although process 200 of FIG. 9 is described in the context of the hardware described herein, process 200 may be performed using any appropriate hardware. The operations shown in process 200 may be performed in the same order as depicted or in a different order, where appropriate.

According to process 200, a treatment plan is stored (201). The treatment plan may be a treatment plan as described above. For example, the treatment plan may specify the type of scanning (e.g., uninterrupted raster scanning) and the total cumulative dose of radiation to be delivered to each location in each layer of an irradiation target. The treatment plan may omit, e.g., the doses to be delivered for each scan at individual locations and their intensities, as well as the number of doses to be delivered to each location and the identity of the locations.

An energy degrader may be set to select (202) a layer, and current may be applied to the magnet and controlled to move (203) the particle beam in accordance with a pattern set forth, e.g., in the treatment plan, to scan the layer. The current control may produce uninterrupted movement of the beam across at least part of the irradiation target to deliver doses of charged particles. An example of a pattern of beam movement 230 across a layer 233 of an irradiation target is shown in FIG. 10 . As the beam moves, each pulse of the beam delivers a dose of radiation to the target. The dose has an intensity, which may be set beforehand in the accelerator or during scanning, and is delivered to specific positions. The exact positions at which dose is to be delivered need not be set beforehand, but rather may be arrived at by a combination of beam movement and pulse output.

For positions at which the dose is delivered, information is stored (204) (or otherwise recorded), which identifies a location and an amount of dose delivered at the location. This information is typically stored after the dose is delivered. As explained above, the information may be determined as dose to delivery of the dose as possible, using the ion chamber to determine particle beam intensity (e.g., the amount of the close) and the current sensor on the scanning magnet to determine the location at which the dose is delivered. As described above, in some implementations, in synchronism with the delivery, information identifying doses of the particle beam delivered to the irradiation target is stored along with at least one of: coordinates at which the doses were delivered or magnet currents at which the doses were delivered. As also described above, this information may be stored in tables, which may be used to store the cumulative dose of radiation applied at positions on various layers of an irradiation target.

The entire layer may be scanned and information therefor recorded, as described above, or only part of the layer may be scanned and information therefor recorded. At a point during scanning, the cumulative dose delivered at each position is compared to a target cumulative dose for that position. For example, this may be done after part of a layer containing that position is scanned, after the entire layer is scanned, after a set of layers are scanned, or after all layers in an irradiation target are scanned. It is determined (205) if the current cumulative dose matches the target cumulative dose at specific positions. If the current cumulative dose does match the target cumulative dose at specific positions, scanning is completed (207) for those positions. If the current cumulative dose does not match the target cumulative dose at specific positions, the scanning system is operated to compensate for deficiencies in the recorded (e.g., current cumulative) doses relative to corresponding target cumulative doses for those positions. For example, if the current cumulative dose does not match the target cumulative dose at specific positions, the current in the scanning magnet may be controlled in order to move (206) the beam so as to deliver additional dose to the specific positions.

As explained above, in some implementations, 100% of the dose may be applied during a single scan (e.g., a single delivery of particles) of a layer. In that case, more than one scan per layer may not be necessary. In other implementations, less than 100% of the dose may be applied during a single scan. In that case, more than one scan per layer will be necessary. To this end, according to the scanning process, for positions at which dose is applied, if the current cumulative dose at each position does not match the target cumulative dose at a corresponding position, the magnet current is controlled in order to move the beam so as to deliver additional dose to positions that require more close. In other words, the layer may be re-scanned any appropriate number of times until the target cumulative dose is reached for all positions of the layer. In some implementations, in one scan or in multiple scans, the actual delivered dose may exceed 100% of the target cumulative dose. What dose to deliver may be dictated by appropriate medical professionals.

As noted above, the layer may be re-scanned at any appropriate point, e.g., after part of the layer is completed with a current scan, after the entire layer is completed with the current scan, after a set of layers is completed with a scan, or after all layers are completed with a scan. During re-scanning, the process above is repeated until the target cumulative dose is reached for all, or some subset of, positions in the irradiation target. In some implementations, the intensity of the particle beam may need to be adjusted, e.g., for the last scan. For example, if the intensity is set at 25% of the target cumulative dose, but only 20% is delivered at each scan, then a fifth (and possibly sixth) dose will require a lower intensity than 25% in order to reach the target cumulative dose.

The processes described herein may be used with a single particle accelerator, and any two or more of the features thereof described herein may be used with the single particle accelerator. The particle accelerator may be used in any type of medical or non-medical application. An example of a particle therapy system that may be used is provided below. Notably, the concepts described herein may be used in other systems not specifically described.

Referring to FIG. 11 , an example implementation of a charged particle radiation therapy system 400 includes a beam-producing particle accelerator 402 (e.g., the particle accelerator of FIGS. 1, 2 ) having a weight and size small enough to permit it to be mounted on a rotating gantry 404 with its output directed straight (that is, essentially directly) from the accelerator housing toward a patient 406. Particle accelerator 402 also includes a scanning system of a type described herein (e.g., FIGS. 3 to 10 ).

In some implementations, the steel gantry has two legs 408, 410 mounted for rotation on two respective bearings 412, 414 that lie on opposite sides of the patient. The accelerator is supported by a steel truss 416 that is long enough to span a treatment area 418 in which the patient lies (e.g., twice as long as a tall person, to permit the person to be rotated fully within the space with any desired target area of the patient remaining in the line of the beam) and is attached stably at both ends to the rotating legs of the gantry.

In some examples, the rotation of the gantry is limited to a range 420 of less than 360 degrees, e.g., about 180 degrees, to permit a floor 422 to extend from a wall of the vault 424 that houses the therapy system into the patient treatment area. The limited rotation range of the gantry also reduces the required thickness of some of the walls (which are not directly aligned with the beam, e.g., wall 430), which provide radiation shielding of people outside the treatment area. A range of 180 degrees of gantry rotation is enough to cover all treatment approach angles, but providing a larger range of travel can be useful. For example the range of rotation may be between 180 and 330 degrees and still provide clearance for the therapy floor space. In other implementations, rotation is not limited as described above.

The horizontal rotational axis 432 of the gantry is located nominally one meter above the floor where the patient and therapist interact with the therapy system. This floor is positioned about 3 meters above the bottom floor of the therapy system shielded vault. The accelerator can swing under the raised floor for delivery of treatment beams from below the rotational axis. The patient couch moves and rotates in a substantially horizontal plane parallel to the rotational axis of the gantry. The couch can rotate through a range 434 of about 270 degrees in the horizontal plane with this configuration. This combination of gantry and patient rotational ranges and degrees of freedom allow the therapist to select virtually any approach angle for the beam. If needed, the patient can be placed on the couch in the opposite orientation and then all possible angles can be used.

In some implementations, the accelerator uses a synchrocyclotron configuration having a high magnetic field superconducting electromagnetic structure. Because the bend radius of a charged particle of a given kinetic energy is reduced in direct proportion to an increase in the magnetic field applied to it, the high magnetic field superconducting magnetic structure permits the accelerator to be made smaller and lighter. The synchrocyclotron uses a magnetic field that is uniform in rotation angle and falls off in strength with increasing radius. Such a field shape can be achieved regardless of the magnitude of the magnetic field, so in theory there is no upper limit to the magnetic field strength (and therefore the resulting particle energy at a fixed radius) that can be used in a synchrocyclotron.

The synchrocyclotron is supported on the gantry so that the beam is generated directly in line with the patient. The gantry permits rotation of the synchrocyclotron about a horizontal rotational axis that contains a point (isocenter 440) within, or near, the patient. The split truss that is parallel to the rotational axis, supports the synchrocyclotron on both sides.

Because the rotational range of the gantry is limited in some example implementations, a patient support area can be accommodated in a wide area around the isocenter. Because the floor can be extended broadly around the isocenter, a patient support table can be positioned to move relative to and to rotate about a vertical axis 442 through the isocenter so that, by a combination of gantry rotation and table motion and rotation, any angle of beam direction into any part of the patient can be achieved. In some implementations, the two gantry arms are separated by more than twice the height of a tall patient, allowing the couch with patient to rotate and translate in a horizontal plane above the raised floor.

Limiting the gantry rotation angle allows for a reduction in the thickness of at least one of the walls surrounding the treatment room. Thick walls, typically constructed of concrete, provide radiation protection to individuals outside the treatment room. A wall downstream of a stopping proton beam may be about twice as thick as a wall at the opposite end of the room to provide an equivalent level of protection. Limiting the range of gantry rotation enables the treatment room to be sited below earth grade on three sides, while allowing an occupied area adjacent to the thinnest wall reducing the cost of constructing the treatment room.

In the example implementation shown in FIG. 11 , the superconducting synchrocyclotron 402 operates with a peak magnetic field in a pole gap of the synchrocyclotron of 8.8 Tesla. The synchrocyclotron produces a beam of protons having an energy of 250 MeV. In some implementations, the synchrocyclotron is a variable-energy machine, and is capable of outputting proton beams having different energies. In some implementations, the synchrocyclotron may produce a beam having a fixed energy. In some implementations the field strength could be in the range of 4 T to 20 T and the proton energy could be in the range of 150 to 300 MeV.

The radiation therapy system described in this example is used for proton radiation therapy, but the same principles and details can be applied in analogous systems for use in heavy ion (ion) treatment systems.

As shown in FIGS. 1, 2, 12, 13, and 14 , an example synchrocyclotron 10 (e.g., 402 in FIG. 11 ) includes a magnet system 122 that contains a particle source 190, a radiofrequency drive system 191, and a beam extraction system. In this example, the magnetic field established by the magnet system has a shape appropriate to maintain focus of a contained proton beam using a combination of a split pair of annular superconducting coils 140, 142 and a pair of shaped ferromagnetic (e.g., low carbon steel) pole faces 144, 146.

The two superconducting magnet coils are centered on a common axis and are spaced apart along the axis. The coils may be formed by of Nb₃Sn-based superconducting 0.8 mm diameter strands (that initially comprise a niobium-tin core surrounded by a copper sheath) deployed in a twisted cable-in-channel conductor geometry. After seven individual strands are cabled together, they are heated to cause a reaction that forms the final (brittle) superconducting material of the wire. After the material has been reacted, the wires are soldered into the copper channel (outer dimensions 3.18×2.54 mm and inner dimensions 2.08×2.08 mm) and covered with insulation (in this example, a woven fiberglass material). The copper channel containing the wires is then wound in a coil having a rectangular cross-section. The wound coil is then vacuum impregnated with an epoxy compound. The finished coils are mounted on an annular stainless steel reverse bobbin. Heater blankets may be placed at intervals in the layers of the windings to protect the assembly in the event of a magnet quench.

The entire coil can then be covered with copper sheets to provide thermal conductivity and mechanical stability and then contained in an additional layer of epoxy. The precompression of the coil can be provided by heating the stainless steel reverse bobbin and fitting the coils within the reverse bobbin. The reverse bobbin inner diameter is chosen so that when the entire mass is cooled to 4 K, the reverse bobbin stays in contact with the coil and provides some compression. Heating the stainless steel reverse bobbin to approximately 50 degrees C. and fitting coils at a temperature of 100 degrees Kelvin can achieve this.

The geometry of the coil is maintained by mounting the coils in a “reverse” rectangular bobbin to exert a restorative force that works against the distorting force produced when the coils are energized. As shown in FIG. 13 , in some implementations, coil position is maintained relative to corresponding magnet pole pieces and the cryostat using a set of warm-to-cold support straps 402, 404, 406. Supporting the cold mass with thin straps reduces the heat leakage imparted to the cold mass by the rigid support system. The straps are arranged to withstand the varying gravitational force on the coil as the magnet rotates on board the gantry. They withstand the combined effects of gravity and the large de-centering force realized by the coil when it is perturbed from a perfectly symmetric position relative to the magnet yoke. Additionally, the links act to reduce dynamic forces imparted on the coil as the gantry accelerates and decelerates when its position is changed. Each warm-to-cold support may include one S2 fiberglass link and one carbon fiber link. The carbon fiber link is supported across pins between the warm yoke and an intermediate temperature (50-70 K), and the S2 fiberglass link 408 is supported across the intermediate temperature pin and a pin attached to the cold mass. Each pin may be made of high strength stainless steel.

Referring to FIG. 1 , the field strength profile as a function of radius is determined largely by choice of coil geometry and pole face shape. The pole faces 144, 146 of the permeable yoke material can be contoured to fine tune the shape of the magnetic field to ensure that the particle beam remains focused during acceleration.

The superconducting coils are maintained at temperatures near absolute zero (e.g., about 4 degrees Kelvin) by enclosing the coil assembly (the coils and the bobbin) inside an evacuated annular aluminum or stainless steel cryostatic chamber 170 (the cryostat) that provides a free space around the coil structure, except at a limited set of support points 171, 173. In an alternate version (e.g., FIG. 2 ) the outer wall of the cryostat may be made of low carbon steel to provide an additional return flux path for the magnetic field.

In some implementations, the temperature near absolute zero is achieved and maintained using one single-stage Gifford-McMahon cryo-cooler and three two-stage Gifford McMahon cryo-coolers. Each two stage cryo-cooler has a second stage cold end attached to a condenser that recondenses Helium vapor into liquid Helium. In some implementations, the temperature near absolute zero is achieved and maintained using a cooling channel (not shown) containing liquid helium, which is formed inside a superconducting coil support structure (e.g., the reverse bobbin), and which contains a thermal connection between the liquid helium in the channel and the corresponding superconducting coil. An example of a liquid helium cooling system of the type described above, and that may be used is described in U.S. patent application Ser. No. 13/148,000 (Begg et al.).

In some implementations, the coil assembly and cryostatic chambers are mounted within and fully enclosed by two halves 181, 183 of a pillbox-shaped magnet yoke 100. The yoke 100 provides a path for the return magnetic field flux 184 and magnetically shields the volume 186 between the pole faces 144, 146 to prevent external magnetic influences from perturbing the shape of the magnetic field within that volume. The yoke also serves to decrease the stray magnetic field in the vicinity of the accelerator. In other implementations, the coil assembly and cryostatic chambers are mounted within and fully enclosed by a non-magnetic enclosure, and the path for return magnetic field flux is implemented using an active return system, an example of which is described above.

As shown in FIGS. 1 and 15 , the synchrocyclotron includes a particle source 190 of a Penning ion gauge geometry located near the geometric center 192 of the magnet structure. The particle source may be as described below, or the particle source may be of the type described in U.S. patent application Ser. No. 11/948,662 incorporated herein by reference.

Particle source 190 is fed from a supply 399 of hydrogen through a gas line 393 and tube 394 that delivers gaseous hydrogen. Electric cables 294 carry an electric current from a current source to stimulate electron discharge from cathodes 392, 390 that are aligned with the magnetic field.

In this example, the discharged electrons ionize the gas exiting through a small hole from tube 394 to create a supply of positive ions (protons) for acceleration by one semicircular (dee-shaped) radio-frequency plate that spans half of the space enclosed by the magnet structure and one dummy dee plate. In the case of an interrupted particle source (an example of which is described in U.S. patent application Ser. No. 11/948,662), all (or a substantial part, e.g., a majority) of the tube containing plasma is removed at the acceleration region.

As shown in FIG. 16 , the dee plate 500 is a hollow metal structure that has two semicircular surfaces 503, 505 that enclose a space 507 in which the protons are accelerated during half of their rotation around the space enclosed by the magnet structure. A duct 509 opening into the space 507 extends through the enclosure (e.g., the yoke or pole piece(s)) to an external location from which a vacuum pump can be attached to evacuate the space 507 and the rest of the space within a vacuum chamber in which the acceleration takes place. The dummy dee 502 comprises a rectangular metal ring that is spaced near to the exposed rim of the dee plate. The dummy dee is grounded to the vacuum chamber and magnet yoke. The dee plate 500 is driven by a radio-frequency signal that is applied at the end of a radio-frequency transmission line to impart an electric field in the space 507. The radio frequency electric field is made to vary in time as the accelerated particle beam increases in distance from the geometric center. The radio frequency electric field may be controlled in the manner described in U.S. patent application Ser. No. 11/948,359, entitled “Matching A Resonant Frequency Of A Resonant Cavity To A Frequency Of An Input Voltage”, the contents of which are incorporated herein by reference.

For the beam emerging from the centrally located particle source to clear the particle source structure as it begins to spiral outward, a large voltage difference may be applied across the radio frequency plates. 20,000 Volts is applied across the radio frequency plates. In some versions from 8,000 to 20,000 Volts may be applied across the radio frequency plates. To reduce the power required to drive this large voltage, the magnet structure is arranged to reduce the capacitance between the radio frequency plates and ground. This may be done by forming holes with sufficient clearance from the radio frequency structures through the outer yoke and the cryostat housing and making sufficient space between the magnet pole faces.

The high voltage alternating potential that drives the dee plate has a frequency that is swept downward during the accelerating cycle to account for the increasing relativistic mass of the protons and the decreasing magnetic field. The dummy dee does not require a hollow semi-cylindrical structure as it is at ground potential along with the vacuum chamber walls. Other plate arrangements could be used such as more than one pair of accelerating electrodes driven with different electrical phases or multiples of the fundamental frequency. The RF structure can be tuned to keep the Q high during the required frequency sweep by using, for example, a rotating capacitor having intermeshing rotating and stationary blades. During each meshing of the blades, the capacitance increases, thus lowering the resonant frequency of the RF structure. The blades can be shaped to create a precise frequency sweep required. A drive motor for the rotating condenser can be phase locked to the RF generator for precise control. One bunch of particles may be accelerated during each meshing of the blades of the rotating condenser.

The vacuum chamber in which the acceleration occurs is a generally cylindrical container that is thinner in the center and thicker at the rim. The vacuum chamber encloses the RF plates and the particle source and is evacuated by a vacuum pump. Maintaining a high vacuum reduces the chances that accelerating ions are not lost to collisions with gas molecules and enables the RF voltage to be kept at a higher level without arcing to ground.

Protons (or other ions) traverse a generally spiral orbital path beginning at the particle source. In half of each loop of the spiral path, the protons gain energy as they pass through the RF electric field. As the protons gain energy, the radius of the central orbit of each successive loop of their spiral path is larger than the prior loop until the loop radius reaches the maximum radius of the pole face. At that location a magnetic and electric field perturbation directs protons into an area where the magnetic field rapidly decreases, and the protons depart the area of the high magnetic field and are directed through an evacuated tube, referred to herein as the extraction channel, to exit the synchrocyclotron. A magnetic regenerator may be used to change the magnetic field perturbation to direct the protons. The protons exiting will tend to disperse as they enter an area of markedly decreased magnetic field that exists in the room around the synchrocyclotron. Beam shaping elements 607, 609 in the extraction channel 138 (FIG. 13 ) redirect the protons so that they stay in a straight beam of limited spatial extent.

As the beam exits the extraction channel it is passed through a beam formation system 525 (FIG. 13 ), which may include a scanning system of the type described herein. Beam formation system 525 may be used in conjunction with an inner gantry that controls application of the beam.

Stray magnetic fields exiting from the synchrocyclotron may be limited by both a magnet yoke (which also serves as a shield) and a separate magnetic shield 514 (e.g., FIG. 1 ). The separate magnetic shield includes of a layer 517 of ferromagnetic material (e.g., steel or iron) that encloses the pillbox yoke, separated by a space 516. This configuration that includes a sandwich of a yoke, a space, and a shield achieves adequate shielding for a given leakage magnetic field at lower weight. As described above, in some implementations, an active return system may be used in place of, or to augment, the operation of the magnetic yoke and shield.

Referring to FIG. 11 , the gantry allows the synchrocyclotron to be rotated about a horizontal rotational axis 432. The truss structure 416 has two generally parallel spans 480, 482. The synchrocyclotron is cradled between the spans about midway between the legs. The gantry is balanced for rotation about the bearings using counterweights 622, 624 mounted on ends of the legs opposite the truss.

The gantry is driven to rotate by an electric motor mounted to one or both of the gantry legs and connected to the bearing housings by drive gears. The rotational position of the gantry is derived from signals provided by shaft angle encoders incorporated into the gantry drive motors and the drive gears.

At the location at which the ion beam exits the synchrocyclotron, the beam formation system 525 acts on the ion beam to give it properties suitable for patient treatment. For example, the beam may be spread and its depth of penetration varied to provide uniform radiation across a given target volume. The beam formation system may include active scanning elements as described herein.

All of the active systems of the synchrocyclotron (the current driven superconducting coils, the RF-driven plates, the vacuum pumps for the vacuum acceleration chamber and for the superconducting coil cooling chamber, the current driven particle source, the hydrogen gas source, and the RF plate coolers, for example), may be controlled by appropriate synchrocyclotron control electronics (not shown), which may include, e.g., one or more processing devices executing instructions from non-transitory memory to effect control.

As explained above, referring to system 602 of FIG. 17 , a beam-producing particle accelerator, in this case synchrocyclotron 604 (which may include any and all features described herein), may be mounted on rotating gantry 605. Rotating gantry 605 is of the type described herein, and can angularly rotate around patient support 606. This feature enables synchrocyclotron 604 to provide a particle beam essentially directly to the patient from various angles. For example, as in FIG. 17 , if synchrocyclotron 604 is above patient support 606, the particle beam may be directed downwards toward the patient. Alternatively, if synchrocyclotron 604 is below patient support 606, the particle beam may be directed upwards toward the patient. The particle beam is applied essentially directly to the patient in the sense that an intermediary beam routing mechanism is not required. A routing mechanism, in this context, is different from a shaping or sizing mechanism in that a shaping or sizing mechanism does not re-route the beam, but rather sizes and/or shapes the beam while maintaining the same general trajectory of the beam.

Further details regarding an example implementation of the foregoing system may be found in U.S. Pat. No. 7,728,311, filed on Nov. 16, 2006 and entitled “Charged Particle Radiation Therapy”, and in U.S. patent application Ser. No. 12/275,103, filed on Nov. 20, 2008 and entitled “Inner Gantry”. The contents of U.S. Pat. No. 7,728,311 and in U.S. patent application Ser. No. 12/275,103 are hereby incorporated by reference into this disclosure. In some implementations, the synchrocyclotron may be a variable-energy device, such as that described in U.S. patent application Ser. No. 13/916,401, filed on Jun. 12, 2013, the contents of which are incorporated herein by reference.

Variable-Energy Particle Accelerator

The particle accelerator used in the example particle therapy systems and example scanning systems described herein may be a variable-energy particle accelerator, an example of which is described below.

The energy of an extracted particle beam (the particle beam output from the accelerator) can affect the use of the particle beam during treatment. In some machines, the energy of the particle beam (or particles in the particle beam) does not increase after extraction. However, the energy may be reduced based on treatment needs after the extraction and before the treatment. Referring to FIG. 18 , an example treatment system 910 includes an accelerator 912, e.g., a synchrocyclotron, from which a particle (e.g., proton) beam 914 having a variable energy is extracted to irradiate a target volume 924 of a body 922. Optionally, one or more additional devices, such as a scanning unit 916 or a scattering unit 916, one or more monitoring units 918, and an energy degrader 920, are placed along the irradiation direction 928. The devices intercept the cross-section of the extracted beam 914 and alter one or more properties of the extracted beam for the treatment.

A target volume to be irradiated (an irradiation target) by a particle beam for treatment typically has a three-dimensional configuration. In some examples, to carry-out the treatment, the target volume is divided into layers along the irradiation direction of the particle beam so that the irradiation can be done on a layer-by-layer basis. For certain types of particles, such as protons, the penetration depth (or which layer the beam reaches) within the target volume is largely determined by the energy of the particle beam. A particle beam of a given energy does not reach substantially beyond a corresponding penetration depth for that energy. To move the beam irradiation from one layer to another layer of the target volume, the energy of the particle beam is changed.

In the example shown in FIG. 18 , the target volume 924 is divided into nine layers 926 a-926 i along the irradiation direction 928. In an example process, the irradiation starts from the deepest layer 926 i, one layer at a time, gradually to the shallower layers and finishes with the shallowest layer 926 a. Before application to the body 922, the energy of the particle beam 914 is controlled to be at a level to allow the particle beam to stop at a desired layer, e.g., the layer 926 d, without substantially penetrating further into the body or the target volume, e.g., the layers 926 e-926 i or deeper into the body. In some examples, the desired energy of the particle beam 914 decreases as the treatment layer becomes shallower relative to the particle acceleration. In some examples, the beam energy difference for treating adjacent layers of the target volume 924 is about 3 MeV to about 100 MeV, e.g., about 10 MeV to about 80 MeV, although other differences may also be possible, depending on, e.g., the thickness of the layers and the properties of the beam.

The energy variation for treating different layers of the target volume 924 can be performed at the accelerator 912 (e.g., the accelerator can vary the energy) so that, in some implementations, no additional energy variation is required after the particle beam is extracted from the accelerator 912. So, the optional energy degrader 920 in the treatment system 10 may be eliminated from the system. In some implementations, the accelerator 912 can output particle beams having an energy that varies between about 100 MeV and about 300 MeV, e.g., between about 115 MeV and about 250 MeV. The variation can be continuous or non-continuous, e.g., one step at a time. In some implementations, the variation, continuous or non-continuous, can take place at a relatively high rate, e.g., up to about 50 MeV per second or up to about 20 MeV per second. Non-continuous variation can take place one step at a time with a step size of about 10 MeV to about 90 MeV.

When irradiation is complete in one layer, the accelerator 912 can vary the energy of the particle beam for irradiating a next layer, e.g., within several seconds or within less than one second. In some implementations, the treatment of the target volume 924 can be continued without substantial interruption or even without any interruption. In some situations, the step size of the non-continuous energy variation is selected to correspond to the energy difference needed for irradiating two adjacent layers of the target volume 924. For example, the step size can be the same as, or a fraction of, the energy difference.

In some implementations, the accelerator 912 and the degrader 920 collectively vary the energy of the beam 914. For example, the accelerator 912 provides a coarse adjustment and the degrader 920 provides a fine adjustment or vice versa. In this example, the accelerator 912 can output the particle beam that varies energy with a variation step of about 10-80 MeV, and the degrader 920 adjusts (e.g., reduces) the energy of the beam at a variation step of about 2-10 MeV.

The reduced use (or absence) of the energy degrader, such as a range modulator, may help to maintain properties and quality of the output beam from the accelerator, e.g., beam intensity. The control of the particle beam can be performed at the accelerator. Side effects, e.g., from neutrons generated when the particle beam passes the degrader 920 can be reduced or eliminated.

The energy of the particle beam 914 may be adjusted to treat another target volume 930 in another body or body part 922′ after completing treatment in target volume 924. The target volumes 924, 930 may be in the same body (or patient), or in different patients. It is possible that the depth D of the target volume 930 from a surface of body 922′ is different from that of the target volume 924. Although some energy adjustment may be performed by the degrader 920, the degrader 912 may only reduce the beam energy and not increase the beam energy.

In this regard, in some cases, the beam energy required for treating target volume 930 is greater than the beam energy required to treat target volume 924. In such cases, the accelerator 912 may increase the output beam energy after treating the target volume 924 and before treating the target volume 930. In other cases, the beam energy required for treating target volume 930 is less than the beam energy required to treat target volume 924. Although the degrader 920 can reduce the energy, the accelerator 912 can be adjusted to output a lower beam energy to reduce or eliminate the use of the degrader 920. The division of the target volumes 924, 930 into layers can be different or the same. The target volume 930 can be treated similarly on a layer by layer basis to the treatment of the target volume 924.

The treatment of the different target volumes 924, 930 on the same patient may be substantially continuous, e.g., with the stop time between the two volumes being no longer than about 30 minutes or less, e.g., 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 5 minutes or less, or 1 minute or less. As explained herein, the accelerator 912 can be mounted on a movable gantry and the movement of the gantry can move the accelerator to aim at different target volumes. In some situations, the accelerator 912 can complete the energy adjustment of the output beam 914 during the time the treatment system makes adjustment (such as moving the gantry) after completing the treatment of the target volume 924 and before starting treating the target volume 930. After the alignment of the accelerator and the target volume 930, the treatment can begin with the adjusted, desired beam energy. Beam energy adjustment for different patients can also be completed relatively efficiently. In some examples, all adjustments, including increasing/reducing beam energy and/or moving the gantry are done within about 30 minutes, e.g., within about 25 minutes, within about 20 minutes, within about 15 minutes, within about 10 minutes or within about 5 minutes.

In the same layer of a target volume, an irradiation dose may be applied by moving the beam across the two-dimensional surface of the layer (which is sometimes called scanning beam) using a scanning unit 916. Alternatively, the layer can be irradiated by passing the extracted beam through one or more scatterers of the scattering unit 16 (which is sometimes called scattering beam).

Beam properties, such as energy and intensity, can be selected before a treatment or can be adjusted during the treatment by controlling the accelerator 912 and/or other devices, such as the scanning unit/scatterer(s) 916, the degrader 920, and others not shown in the figures. In example implementations, system 910 includes a controller 932, such as a computer, in communication with one or more devices in the system. Control can be based on results of the monitoring performed by the one or more monitors 918, e.g., monitoring of the beam intensity, close, beam location in the target volume, etc. Although the monitors 918 are shown to be between the device 916 and the degrader 920, one or more monitors can be placed at other appropriate locations along the beam irradiation path. Controller 932 can also store a treatment plan for one or more target volumes (for the same patient and/or different patients). The treatment plan can be determined before the treatment starts and can include parameters, such as the shape of the target volume, the number of irradiation layers, the irradiation dose for each layer, the number of times each layer is irradiated, etc. The adjustment of a beam property within the system 910 can be performed based on the treatment plan. Additional adjustment can be made during the treatment, e.g., when deviation from the treatment plan is detected.

In some implementations, the accelerator 912 is configured to vary the energy of the output particle beam by varying the magnetic field in which the particle beam is accelerated. In an example implementation, one or more sets of coils receives variable electrical current to produce a variable magnetic field in the cavity. In some examples, one set of coils receives a fixed electrical current, while one or more other sets of coils receives a variable current so that the total current received by the coil sets varies. In some implementations, all sets of coils are superconducting. In other implementations, some sets of coils, such as the set for the fixed electrical current, are superconducting, while other sets of coils, such as the one or more sets for the variable current, are non-superconducting. In some examples, all sets of coils are non-superconducting.

Generally, the magnitude of the magnetic field is scalable with the magnitude of the electrical current. Adjusting the total electric current of the coils in a predetermined range can generate a magnetic field that varies in a corresponding, predetermined range. In some examples, a continuous adjustment of the electrical current can lead to a continuous variation of the magnetic field and a continuous variation of the output beam energy. Alternatively, when the electrical current applied to the coils is adjusted in a non-continuous, step-wise manner, the magnetic field and the output beam energy also varies accordingly in a non-continuous (step-wise) manner. The scaling of the magnetic field to the current can allow the variation of the beam energy to be carried out relatively precisely, although sometimes minor adjustment other than the input current may be performed.

In some implementations, to output particle beams having a variable energy, the accelerator 912 is configured to apply RF voltages that sweep over different ranges of frequencies, with each range corresponding to a different output beam energy. For example, if the accelerator 912 is configured to produce three different output beam energies, the RF voltage is capable of sweeping over three different ranges of frequencies. In another example, corresponding to continuous beam energy variations, the RF voltage sweeps over frequency ranges that continuously change. The different frequency ranges may have different lower frequency and/or upper frequency boundaries.

The extraction channel may be configured to accommodate the range of different energies produced by the variable-energy particle accelerator. For example the extraction channel may be large enough to support the highest and lowest energies produced by the particle accelerator. That is, the extraction channel may be sized or otherwise configured to receive and to transmit particles within that range of energies. Particle beams having different energies can be extracted from the accelerator 912 without altering the features of the regenerator that is used for extracting particle beams having a single energy. In other implementations, to accommodate the variable particle energy, the regenerator can be moved to disturb (e.g., change) different particle orbits in the manner described above and/or iron rods (magnetic shims) can be added or removed to change the magnetic field bump provided by the regenerator. More specifically, different particle energies will typically be at different particle orbits within the cavity. By moving the regenerator, it is possible to intercept a particle orbit at a specified energy and thereby provide the correct perturbation of that orbit so that particles at the specified energy reach the extraction channel. In some implementations, movement of the regenerator (and/or addition/removal of magnetic shims) is performed in real-time to match real-time changes in the particle beam energy output by the accelerator. In other implementations, particle energy is adjusted on a per-treatment basis, and movement of the regenerator (and/or addition/removal of magnetic shims) is performed in advance of the treatment. In either case, movement of the regenerator (and/or addition/removal of magnetic shims) may be computer controlled. For example, a computer may control one or more motors that effect movement of the regenerator and/or magnetic shims.

In some implementations, the regenerator is implemented using one or more magnetic shims that are controllable to move to the appropriate location(s).

As an example, table 1 shows three example energy levels at which example accelerator 912 can output particle beams. The corresponding parameters for producing the three energy levels are also listed. In this regard, the magnet current refers to the total electrical current applied to the one or more coil sets in the accelerator 912; the maximum and minimum frequencies define the ranges in which the RF voltage sweeps; and “r” is the radial distance of a location to a center of the cavity in which the particles are accelerated.

TABLE 1 Examples of beam energies and respective parameters. Magnetic Beam Magnet Maximum Minimum Magnetic Field Field at Energy Current Frequency Frequency at r = 0 mm r = 298 mm (MeV) (Amps) (MHz) (MHz) (Tesla) (Tesla) 250 1990 132 99 8.7 8.2 235 1920 128 97 8.4 8.0 211 1760 120 93 7.9 7.5

Details that may be included in an example particle accelerator that produces charged particles having variable energies are described below. The accelerator can be a synchrocyclotron and the particles may be protons. The particles may be output as pulsed beams. The energy of the beam output from the particle accelerator can be varied during the treatment of one target volume in a patient, or between treatments of different target volumes of the same patient or different patients. In some implementations, settings of the accelerator are changed to vary the beam energy when no beam (or particles) is output from the accelerator. The energy variation can be continuous or non-continuous over a desired range.

Referring to the example shown in FIG. 1 , the particle accelerator, which may be a variable-energy particle accelerator like accelerator 912 described above, may be configured to output particle beams that have a variable energy. The range of the variable energy can have an upper boundary that is about 200 MeV to about 300 MeV or higher, e.g., 200 MeV, about 205 MeV, about 210 MeV, about 215 MeV, about 220 MeV, about 225 MeV, about 230 MeV, about 235 MeV, about 240 MeV, about 245 MeV, about 250 MeV, about 255 MeV, about 260 MeV, about 265 MeV, about 270 MeV, about 275 MeV, about 280 MeV, about 285 MeV, about 290 MeV, about 295 MeV, or about 300 MeV or higher. The range can also have a lower boundary that is about 100 MeV or lower to about 200 MeV, e.g., about 100 MeV or lower, about 105 MeV, about 110 MeV, about 115 MeV, about 120 MeV, about 125 MeV, about 130 MeV, about 135 MeV, about 140 MeV, about 145 MeV, about 150 MeV, about 155 MeV, about 160 MeV, about 165 MeV, about 170 MeV, about 175 MeV, about 180 MeV, about 185 MeV, about 190 MeV, about 195 MeV, about 200 MeV.

In some examples, the variation is non-continuous and the variation step can have a size of about 10 MeV or lower, about 15 MeV, about 20 MeV, about 25 MeV, about 30 MeV, about 35 MeV, about 40 MeV, about 45 MeV, about 50 MeV, about 55 MeV, about 60 MeV, about 65 MeV, about 70 MeV, about 75 MeV, or about 80 MeV or higher. Varying the energy by one step size can take no more than 30 minutes, e.g., about 25 minutes or less, about 20 minutes or less, about 15 minutes or less, about 10 minutes or less, about 5 minutes or less, about 1 minute or less, or about 30 seconds or less. In other examples, the variation is continuous and the accelerator can adjust the energy of the particle beam at a relatively high rate, e.g., up to about 50 MeV per second, up to about 45 MeV per second, up to about 40 MeV per second, up to about 35 MeV per second, up to about 30 MeV per second, up to about 25 MeV per second, up to about 20 MeV per second, up to about 15 MeV per second, or up to about 10 MeV per second. The accelerator can be configured to adjust the particle energy both continuously and non-continuously. For example, a combination of the continuous and non-continuous variation can be used in a treatment of one target volume or in treatments of different target volumes. Flexible treatment planning and flexible treatment can be achieved.

A particle accelerator that outputs a particle beam having a variable energy can provide accuracy in irradiation treatment and reduce the number of additional devices (other than the accelerator) used for the treatment. For example, the use of degraders for changing the energy of an output particle beam may be reduced or eliminated for all or part of the treatment. The properties of the particle beam, such as intensity, focus, etc. can be controlled at the particle accelerator and the particle beam can reach the target volume without substantial disturbance from the additional devices. The relatively high variation rate of the beam energy can reduce treatment time and allow for efficient use of the treatment system.

In some implementations, the accelerator, such as the synchrocyclotron of FIG. 1 , accelerates particles or particle beams to variable energy levels by varying the magnetic field in the accelerator, which can be achieved by varying the electrical current applied to coils for generating the magnetic field. As explained above, an example synchrocyclotron (e.g., the synchrocyclotron of FIG. 1 ) includes a magnet system that contains a particle source, a radiofrequency drive system, and a beam extraction system. FIG. 19 shows an example of a magnet system that may be used in a variable-energy accelerator. In this example implementation, the magnetic field established by the magnet system 1012 can vary by about 5% to about 35% of a maximum value of the magnetic field that two sets of coils 40 a and 40 b, and 42 a and 42 b are capable of generating. The magnetic field established by the magnet system has a shape appropriate to maintain focus of a contained proton beam using a combination of the two sets of coils and a pair of shaped ferromagnetic (e.g., low carbon steel) structures, examples of which are provided above.

Each set of coils may be a split pair of annular coils to receive electrical current. In some situations, both sets of coils are superconducting. In other situations, only one set of the coils is superconducting and the other set is non-superconducting or normal conducting (also discussed further below). It is also possible that both sets of coils are non-superconducting. Suitable superconducting materials for use in the coils include niobium-3 tin (Nb3Sn) and/or niobium-titanium. Other normal conducting materials can include copper. Examples of the coil set constructions are described further below.

The two sets of coils can be electrically connected serially or in parallel. In some implementations, the total electrical current received by the two sets of coils can include about 2 million ampere turns to about 10 million ampere turns, e.g., about 2.5 to about 7.5 million ampere turns or about 3.75 million ampere turns to about 5 million ampere turns. In some examples, one set of coils is configured to receive a fixed (or constant) portion of the total variable electrical current, while the other set of coils is configured to receive a variable portion of the total electrical current. The total electrical current of the two coil sets varies with the variation of the current in one coil set. In other situations, the electrical current applied to both sets of coils can vary. The variable total current in the two sets of coils can generate a magnetic field having a variable magnitude, which in turn varies the acceleration pathways of the particles and produces particles having variable energies.

Generally, the magnitude of the magnetic field generated by the coil(s) is scalable to the magnitude of the total electrical current applied to the coil(s). Based on the scalability, in some implementations, linear variation of the magnetic field strength can be achieved by linearly changing the total current of the coil sets. The total current can be adjusted at a relatively high rate that leads to a relatively high-rate adjustment of the magnetic field and the beam energy.

In the example reflected in Table 1 above, the ratio between values of the current and the magnetic field at the geometric center of the coil rings is: 1990:8.7 (approximately 228.7:1); 1920:8.4 (approximately 228.6:1); 1760:7.9 (approximately 222.8:1). Accordingly, adjusting the magnitude of the total current applied to a superconducting coil(s) can proportionally (based on the ratio) adjust the magnitude of the magnetic field.

The scalability of the magnetic field to the total electrical current in the example of Table 1 is also shown in the plot of FIG. 20 , where BZ is the magnetic field along the Z direction; and R is the radial distance measured from a geometric center of the coil rings along a direction perpendicular to the Z direction. The magnetic field has the highest value at the geometric center, and decreases as the distance R increases. The curves 1035, 1037 represent the magnetic field generated by the same coil sets receiving different total electrical current: 1760 Amperes and 1990 Amperes, respectively. The corresponding energies of the extracted particles are 211 MeV and 250 MeV, respectively. The two curves 1035, 1037 have substantially the same shape and the different parts of the curves 1035, 1037 are substantially parallel. As a result, either the curve 1035 or the curve 1037 can be linearly shifted to substantially match the other curve, indicating that the magnetic field is scalable to the total electrical current applied to the coil sets.

In some implementations, the scalability of the magnetic field to the total electrical current may not be perfect. For example, the ratio between the magnetic field and the current calculated based on the example shown in table 1 is not constant. Also, as shown in FIG. 21 , the linear shift of one curve may not perfectly match the other curve. In some implementations, the total current is applied to the coil sets under the assumption of perfect scalability. The target magnetic field (under the assumption of perfect scalability) can be generated by additionally altering the features, e.g., geometry, of the coils to counteract the imperfection in the scalability. As one example, ferromagnetic (e.g., iron) rods (magnetic shims) can be inserted or removed from one or both of the magnetic structures (e.g., yokes, pole pieces, and the like). The features of the coils can be altered at a relatively high rate so that the rate of the magnetic field adjustment is not substantially affected as compared to the situation in which the scalability is perfect and only the electrical current needs to be adjusted. In the example of iron rods, the rods can be added or removed at the time scale of seconds or minutes, e.g., within 5 minutes, within 1 minute, less than 30 seconds, or less than 1 second.

In some implementations, settings of the accelerator, such as the current applied to the coil sets, can be chosen based on the substantial scalability of the magnetic field to the total electrical current in the coil sets.

Generally, to produce the total current that varies within a desired range, any appropriate combination of current applied to the two coil sets can be used. In an example, the coil set 42 a, 42 b can be configured to receive a fixed electrical current corresponding to a lower boundary of a desired range of the magnetic field. In the example shown in table 1, the fixed electrical current is 1760 Amperes. In addition, the coil set 40 a, 40 b can be configured to receive a variable electrical current having an upper boundary corresponding to a difference between an upper boundary and a lower boundary of the desired range of the magnetic field. In the example shown in table 1, the coil set 40 a, 40 b is configured to receive electrical current that varies between 0 Ampere and 230 Amperes.

In another example, the coil set 42 a, 42 b can be configured to receive a fixed electrical current corresponding to an upper boundary of a desired range of the magnetic field. In the example shown in table 1, the fixed current is 1990 Amperes. In addition, the coil set 40 a, 40 b can be configured to receive a variable electrical current having an upper boundary corresponding to a difference between a lower boundary and an upper boundary of the desired range of the magnetic field. In the example shown in table 1, the coil set 40 a, 40 b is configured to receive electrical current that varies between −230 Ampere and 0 Ampere.

The total variable magnetic field generated by the variable total current for accelerating the particles can have a maximum magnitude greater than 4 Tesla, e.g., greater than 5 Tesla, greater than 6 Tesla, greater than 7 Tesla, greater than 8 Tesla, greater than 9 Tesla, or greater than 10 Tesla, and up to about 20 Tesla or higher, e.g., up to about 18 Tesla, up to about 15 Tesla, or up to about 12 Tesla. In some implementations, variation of the total current in the coil sets can vary the magnetic field by about 0.2 Tesla to about 4.2 Tesla or more, e.g., about 0.2 Tesla to about 1.4 Tesla or about 0.6 Tesla to about 4.2 Tesla. In some situations, the amount of variation of the magnetic field can be proportional to the maximum magnitude.

FIG. 21 shows an example RF structure for sweeping the voltage on the dee plate 500 over an RF frequency range for each energy level of the particle beam, and for varying the frequency range when the particle beam energy is varied. The semicircular surfaces 503, 505 of the dee plate 500 are connected to an inner conductor 1300 and housed in an outer conductor 1302. The high voltage is applied to the dee plate 500 from a power source (not shown, e.g., an oscillating voltage input) through a power coupling device 1304 that couples the power source to the inner conductor. In some implementations, the coupling device 1304 is positioned on the inner conductor 1300 to provide power transfer from the power source to the dee plate 500. In addition, the dee plate 500 is coupled to variable reactive elements 1306, 1308 to perform the RF frequency sweep for each particle energy level, and to change the RF frequency range for different particle energy levels.

The variable reactive element 1306 can be a rotating capacitor that has multiple blades 1310 rotatable by a motor (not shown). By meshing or unmeshing the blades 1310 during each cycle of RF sweeping, the capacitance of the RF structure changes, which in turn changes the resonant frequency of the RF structure. In some implementations, during each quarter cycle of the motor, the blades 1310 mesh with the each other. The capacitance of the RF structure increases and the resonant frequency decreases. The process reverses as the blades 1310 unmesh. As a result, the power required to generate the high voltage applied to the dee plate 103 and necessary to accelerate the beam can be reduced by a large factor. In some implementations, the shape of the blades 1310 is machined to form the required dependence of resonant frequency on time.

The RF frequency generation is synchronized with the blade rotation by sensing the phase of the RF voltage in the resonator, keeping the alternating voltage on the dee plates dose to the resonant frequency of the RF cavity. (The dummy dee is grounded and is not shown in FIG. 21 ).

The variable reactive element 1308 can be a capacitor formed by a plate 1312 and a surface 1316 of the inner conductor 1300. The plate 1312 is movable along a direction 1314 towards or away from the surface 1316. The capacitance of the capacitor changes as the distance D between the plate 1312 and the surface 1316 changes. For each frequency range to be swept for one particle energy, the distance D is at a set value, and to change the frequency range, the plate 1312 is moved corresponding to the change in the energy of the output beam.

In some implementations, the inner and outer conductors 1300, 1302 are formed of a metallic material, such as copper, aluminum, or silver. The blades 1310 and the plate 1312 can also be formed of the same or different metallic materials as the conductors 1300, 1302. The coupling device 1304 can be an electrical conductor. The variable reactive elements 1306, 1308 can have other forms and can couple to the dee plate 100 in other ways to perform the RF frequency sweep and the frequency range alteration. In some implementations, a single variable reactive element can be configured to perform the functions of both the variable reactive elements 1306, 1308. In other implementations, more than two variable reactive elements can be used.

The control of the gantry, the patient support, the active beam shaping elements, and the synchrocyclotron to perform a therapy session is achieved by appropriate therapy control electronics (not shown).

Control of the particle therapy system described herein and its various features may be implemented using hardware or a combination of hardware and software. For example, a system like the ones described herein may include various controllers and/or processing devices located at various points. A central computer may coordinate operation among the various controllers or processing devices. The central computer, controllers, and processing devices may execute various software routines to effect control and coordination of testing and calibration.

System operation can be controlled, at least in part, using one or more computer program products, e.g., one or more computer program tangibly embodied in one or more non-transitory machine-readable media, for execution by, or to control the operation of, one or more data processing apparatus, e.g., a programmable processor, a computer, multiple computers, and/or programmable logic components.

A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a network.

Actions associated with implementing all or part of the operations of the particle therapy system described herein can be performed by one or more programmable processors executing one or more computer programs to perform the functions described herein. All or part of the operations can be implemented using special purpose logic circuitry, e.g., an FPGA (field programmable gate array) and/or an ASIC (application-specific integrated circuit).

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only storage area or a random access storage area or both. Elements of a computer (including a server) include one or more processors for executing instructions and one or more storage area devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from, or transfer data to, or both, one or more machine-readable storage media, such as mass PCBs for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Non-transitory machine-readable storage media suitable for embodying computer program instructions and data include all forms of non-volatile storage area, including by way of example, semiconductor storage area devices, e.g., EPROM, EEPROM, and flash storage area devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

Any “electrical connection” as used herein may imply a direct physical connection or a connection that includes intervening components but that nevertheless allows electrical signals to flow between connected components. Any “connection” involving electrical circuitry mentioned herein, unless stated otherwise, is an electrical connection and not necessarily a direct physical connection regardless of whether the word “electrical” is used to modify “connection”.

Any two more of the foregoing implementations may be used in an appropriate combination in an appropriate particle accelerator (e.g., a synchrocyclotron). Likewise, individual features of any two more of the foregoing implementations may be used in an appropriate combination.

Elements of different implementations described herein may be combined to form other implementations not specifically set forth above. Elements may be left out of the processes, systems, apparatus, etc., described herein without adversely affecting their operation. Various separate elements may be combined into one or more individual elements to perform the functions described herein.

The example implementations described herein are not limited to use with a particle therapy system or to use with the example particle therapy systems described herein. Rather, the example implementations can be used in any appropriate system that directs accelerated particles to an output.

Additional information concerning the design of an example implementation of a particle accelerator that may be used in a system as described herein can be found in U.S. Provisional Application No. 60/760,788, entitled “High-Field Superconducting Synchrocycloton” and filed Jan. 20, 2006; U.S. patent application Ser. No. 11/463,402, entitled “Magnet Structure For Particle Acceleration” and filed Aug. 9, 2006; and U.S. Provisional Application No. 60/850,565, entitled “Cryogenic Vacuum Break Pneumatic Thermal Coupler” and filed Oct. 10, 2006, all of which are incorporated herein by reference.

The following applications are incorporated by reference into the subject application: the U.S. Provisional Application entitled “CONTROLLING INTENSITY OF A PARTICLE BEAM” (Application No. 61/707,466), the U.S. Provisional Application entitled “ADJUSTING ENERGY OF A PARTICLE BEAM” (Application No. 61/707,515), the U.S. Provisional Application entitled “ADJUSTING COIL POSITION” (Application No. 61/707,548), the U.S. Provisional Application entitled “FOCUSING A PARTICLE BEAM USING MAGNETIC FIELD FLUTTER” (Application No. 61/707,572), the U.S. Provisional Application entitled “MAGNETIC FIELD REGENERATOR” (Application No. 61/707,590), the U.S. Provisional Application entitled “FOCUSING A PARTICLE BEAM” (Application No. 61/707,704), the U.S. Provisional Application entitled “CONTROLLING PARTICLE THERAPY (Application No. 61/707,624), and the U.S. Provisional Application entitled “CONTROL SYSTEM FOR A PARTICLE ACCELERATOR” (Application No. 61/707,645).

The following are also incorporated by reference into the subject application: U.S. Pat. No. 7,728,311 which issued on Jun. 1, 2010, U.S. patent application Ser. No. 11/948,359 which was filed on Nov. 30, 2007, U.S. patent application Ser. No. 12/275,103 which was filed on Nov. 20, 2008, U.S. patent application Ser. No. 11/948,662 which was filed on Nov. 30, 2007, U.S. Provisional Application No. 60/991,454 which was filed on Nov. 30, 2007, U.S. Pat. No. 8,003,964 which issued on Aug. 23, 2011, U.S. Pat. No. 7,208,748 which issued on Apr. 24, 2007, U.S. Pat. No. 7,402,963 which issued on Jul. 22, 2008, U.S. patent application Ser. No. 13/148,000 filed Feb. 9, 2010, U.S. patent application Ser. No. 11/937,573 filed on Nov. 9, 2007, U.S. patent application Ser. No. 11/187,633, titled “A Programmable Radio Frequency Waveform Generator for a Synchrocyclotron,” filed Jul. 21, 2005, U.S. Provisional Application No. 60/590,089, filed on Jul. 21, 2004, U.S. patent application Ser. No. 10/949,734, titled “A Programmable Particle Scatterer for Radiation Therapy Beam Formation”, filed Sep. 24, 2004, and U.S. Provisional Application No. 60/590,088, filed Jul. 21, 2005.

Any features of the subject application may be combined with one or more appropriate features of the following: the U.S. Provisional Application entitled “CONTROLLING INTENSITY OF A PARTICLE BEAM” (Application No. 61/707,466), the U.S. Provisional Application entitled “ADJUSTING ENERGY OF A PARTICLE BEAM” (Application No. 61/707,515), the U.S. Provisional Application entitled “ADJUSTING COIL POSITION” (Application No. 61/707,548), the U.S. Provisional Application entitled “FOCUSING A PARTICLE BEAM USING MAGNETIC FIELD FLUTTER” (Application No. 61/707,572), the U.S. Provisional Application entitled “MAGNETIC FIELD REGENERATOR” (Application No. 61/707,590), the U.S. Provisional Application entitled “FOCUSING A PARTICLE BEAM” (Application No. 61/707,704), the U.S. Provisional Application entitled “CONTROLLING PARTICLE THERAPY (Application No. 61/707,624), and the U.S. Provisional Application entitled “CONTROL SYSTEM FOR A PARTICLE ACCELERATOR” (Application No. 61/707,645), U.S. Pat. No. 7,728,311 which issued on Jun. 1, 2010, U.S. patent application Ser. No. 11/948,359 which was filed on Nov. 30, 2007, U.S. patent application Ser. No. 12/275,103 which was filed on Nov. 20, 2008, U.S. patent application Ser. No. 11/948,662 which was filed on Nov. 30, 2007, U.S. Provisional Application No. 60/991,454 which was filed on Nov. 30, 2007, U.S. patent application Ser. No. 13/907,601, which was filed on May 31, 2013, U.S. patent application Ser. No. 13/916,401, filed on Jun. 12, 2013, U.S. Pat. No. 8,003,964 which issued on Aug. 23, 2011, U.S. Pat. No. 7,208,748 which issued on Apr. 24, 2007, U.S. Pat. No. 7,402,963 which issued on Jul. 22, 2008, U.S. patent application Ser. No. 13/148,000 filed Feb. 9, 2010, U.S. patent application Ser. No. 11/937,573 filed on Nov. 9, 2007, U.S. patent application Ser. No. 11/187,633, titled “A Programmable Radio Frequency Waveform Generator for a Synchrocyclotron,” filed Jul. 21, 2005, U.S. Provisional Application No. 60/590,089, filed on Jul. 21, 2004, U.S. patent application Ser. No. 10/949,734, titled “A Programmable Particle Scatterer for Radiation Therapy Beam Formation”, filed Sep. 24, 2004, and U.S. Provisional Application No. 60/590,088, filed Jul. 21, 2005.

Other implementations not specifically described herein are also within the scope of the following claims. 

What is claimed is:
 1. A synchrocyclotron comprising: a voltage source to provide a radio frequency (RF) voltage to a cavity to accelerate particles within the cavity; one or more coils to pass electrical current having one of multiple values and to generate a magnetic field in the cavity corresponding to the electrical current; magnetic pole pieces at least partly defining the cavity to shape the magnetic field, the magnetic pole pieces comprising ferromagnetic material; wherein the synchrocyclotron is configured to enable setting of the electrical current to one of the multiple values, each of the multiple values corresponding to a different energy at which particles are output from the synchrocyclotron; and wherein the RF voltage is controllable to sweep over different frequency ranges, each different frequency range corresponding to a different energy at which particles are output from the cavity; and wherein the synchrocyclotron further comprises: a variable reactive element comprising a conductive plate that is movable towards or away from a conductor, the variable reactive element for controlling the RF voltage; and a capacitor having blades configured to rotate in order to mesh and ummesh and thereby change a resonant frequency of the cavity.
 2. The synchrocyclotron of claim 1, wherein the one or more coils comprise a first coil and a second coil; and wherein the electrical current comprises a first electrical current that is fixed to pass through the first coil and a second electrical current that is changeable to take on one of multiple values to pass through the second coil, the second electrical current being within a range to cause the magnetic field at an extraction radius of the synchrocyclotron to be between 5% and 35% of a value of the magnetic field in the cavity.
 3. The synchrocyclotron of claim 2, wherein the magnetic field at the extraction radius is changeable by between about 0.2 Testa and about 1.4 Testa.
 4. The synchrocyclotron of claim 2, wherein the magnetic field at the extraction radius is changeable by between about 0.6 and about 4.2 Tesla.
 5. The synchrocyclotron of claim 1, wherein the one or more coils comprises a first set of coils and a second set of coils, the first set being configured to receive a fixed electrical current, and the second set being configured to receive electrical current that is changeable to take on one of multiple values.
 6. The synchrocyclotron of claim 5, wherein the electrical current that is changeable to take on one of multiple values is within a range that causes the magnetic field at an extraction radius of the synchrocyclotron to change by between 5% and 35% of a value of the magnetic field in the cavity.
 7. The synchrocyclotron of claim 6, wherein the magnetic field at the extraction radius is changeable by between about 0.2 Tesla and about 1.4 Tesla or between about 0.6 and about 4.2 Tesla.
 8. The synchrocyclotron of claim 1, wherein the one or more coils comprises a set of coils, the set of coils comprising superconducting coils.
 9. The synchrocyclotron of claim 1, wherein the magnetic field has a magnitude having a range of about 4 Tesla to about 20 Tesla in the cavity.
 10. The synchrocyclotron of claim 1, wherein the energy of the particles that are output from the cavity is variable continuously between about 115 MeV and about 250 MeV.
 11. The synchrocyclotron of claim 10, wherein the energy of the particles that are output from the cavity is variable at a rate up to 20 MeV per second.
 12. The synchrocyclotron of claim 1, wherein the energy of the particles that are output from the cavity is variable non-continuously between about 115 MeV and about 250 MeV.
 13. The synchrocyclotron of claim 12, wherein the energy of the particles is variable at a step size of about 10 MeV to about 80 MeV.
 14. The synchrocyclotron of claim 13, wherein each variation of the energy by one step takes less than 30 minutes.
 15. The synchrocyclotron of claim 1, wherein the one or more coils comprises a superconducting coil.
 16. A system comprising the synchrocyclotron of claim 1, wherein the particles output from the synchrocyclotron form a beam of particles; and wherein the system comprises: a scanning system to perform scanning on at least part of an irradiation target, the scanning system comprising a scanning magnet to move the beam across the at least part of the irradiation target during scanning, where movement of the beam is based on a current of the scanning magnet; and a control system (i) to control the current of the scanning magnet independently of an RF cycle of the RF voltage in order to move the beam across the at least part of the irradiation target to deliver doses of charged particles, (ii) for positions on the irradiation target at which the particle beam delivers a dose of charged particles, to store information identifying a location and an amount of the dose delivered, (iii) to compare a cumulative dose delivered at each position to a target cumulative dose, and (iv) if the cumulative dose does not match the target cumulative dose at specific positions, to control the current of the scanning magnet in order to move the beam so as to deliver additional dose to the specific positions.
 17. A system comprising the synchrocyclotron of claim 1, wherein the particles output from the synchrocyclotron form a beam of particles; and wherein the system comprises: a scanning system to perform scanning on least part of an irradiation target, the scanning system comprising a scanning magnet to move the beam across the at least part of the irradiation target during scanning, where movement of the beam is based on a current of the scanning magnet; and a control system (i) to control the current of the scanning magnet independently of an RF cycle of the RF voltage in order to move the beam across the at least part of the irradiation target so as to deliver doses of charged particles to positions on the irradiation target; and (ii) to determine, in synchronism with delivery of a dose of charged particles to a position on the irradiation target, information identifying an amount of the dose actually delivered to the position.
 18. The synchrocyclotron of claim 1, wherein each frequency range comprises a lower boundary and an upper boundary, and wherein the lower boundary is within a range of about 40 MHz to about 250 MHz, and the upper boundary is within a range of about 56 MHz to about 340 MHz.
 19. The synchrocyclotron of claim 18, wherein the lower boundary is within a range of about 73 MHz to about 150 MHz, and the upper boundary is within a range of about 131 MHz to about 196 MHz.
 20. The synchrocyclotron of claim 1, wherein the one or more coils comprises a first set of coils and a second set of coils, the first set of coils being superconducting and configured to receive a fixed electrical current, and the second set of coils comprise superconducting or non-superconducting and configured to receive electrical current that is changeable to take on one of multiple values.
 21. A proton therapy system comprising: the synchrocyclotron of claim 1; and a gantry on which the synchrocyclotron is mounted, the gantry being rotatable relative to a patient position; wherein the particles are protons and the proton therapy system is configured to output the protons from the synchrocyclotron towards the patient position.
 22. The synchrocyclotron of claim 1, further comprising: one or more ferromagnetic rods that are movable relative to the magnetic pole pieces in order to affect a value of the magnetic field.
 23. A synchrocyclotron comprising: a voltage source to provide a radio frequency (RF) voltage to a cavity to accelerate particles from a particle source; coils comprising a first set of coils and a second set of coils, the first set of coils to pass a first electrical current, and the second set of coils to pass a second electrical current, the first electrical current being fixed and the second electrical current being changeable to take on one of multiple values, the coils to generate a magnetic field to cause the particles to move orbitally within the cavity; an extraction channel to receive the particles from the cavity, and to output the particles from the synchrocyclotron; a variable reactive element comprising a conductive plate that is movable towards or away from a conductor, the variable reactive element for controlling the RF voltage to sweep over different frequency ranges within the cavity; and a capacitor having blades configured to rotate in order to mesh and unmesh and thereby change a resonant frequency of the cavity.
 24. The synchrocyclotron of claim 23, wherein the second electrical current is within a range that causes the magnetic field at an extraction radius of the synchrocyclotron to change by between 5% and 35% of a value of the magnetic field in the cavity.
 25. The synchrocyclotron of claim 24, wherein the magnetic field at the extraction radius is changeable by between about 0.2 Tesla and about 1.4 Testa or between about 0.6 and about 4.2 Tesla.
 26. The synchrocyclotron of claim 23, wherein the magnetic field has a magnitude having a range of about 4 Tesla to about 20 Tesla in the cavity.
 27. The synchrocyclotron of claim 23, further comprising: magnetic pole pieces that border the cavity; and one or more ferromagnetic rods that are movable relative to the magnetic pole pieces in order to affect a value of the magnetic field.
 28. The synchrocyclotron of claim 27, wherein the one or more ferromagnetic rods are movable within at least one of the magnetic pole pieces.
 29. A system comprising the synchrocyclotron of claim 23, wherein the particles from the cavity form a beam of particles; and wherein the system comprises: a scanning system to perform scanning on at least part of an irradiation target, the scanning system comprising a scanning magnet to move the beam across the at least part of the irradiation target during scanning, where movement of the beam is based on a current of the scanning magnet; and a control system (i) to control the current of the scanning magnet independently of an RF cycle of the RF voltage in order to move the beam across the at least part of the irradiation target to deliver doses of charged particles, (ii) for positions on the irradiation target at which the particle beam delivers a dose of charged particles, to store information identifying a location and an amount of the dose delivered, (iii) to compare a cumulative dose delivered at each position to a target cumulative dose, and (iv) if the cumulative dose does not match the target cumulative dose at specific positions, to control the current of the scanning magnet in order to move the beam so as to deliver additional dose to the specific positions.
 30. A system comprising the synchrocyclotron of claim 23, wherein the particles from the cavity form a beam of particles; and wherein the system comprises: a scanning system to perform scanning on least part of an irradiation target, the scanning system comprising a scanning magnet to move the beam across the at least part of the irradiation target during scanning, where movement of the beam is based on a current of the scanning magnet; and a control system (i) to control the current of the scanning magnet independently of an RF cycle of the RF voltage in order to move the beam across the at least part of the irradiation target so as to deliver doses of charged particles to positions on the irradiation target; and (ii) to determine, in synchronism with delivery of a dose of charged particles to a position on the irradiation target, information identifying an amount of the dose actually delivered to the position. 